Opinion:
Is spending the time to train to level 5, especially for weapons Specialization, really always necessary?
It seems most weapons specialty skills need spending 20-30+ days training to get from level 4 to 5 just to give 1-2-3% bonus.
I know every little bit can help, but it certainly would speed up my training schedule to postpone 4->5.
Thanks
No. Level V is sometimes nessessary to unlock other skills or modules or in some doctrines to make fits/setups work (Logis, Energy Transfer etc…). But for a beginner that still needs to care what he skills first, Level IV on all the stuff you can use is enough for 90% of all usecases.
Thats why the Magic 14 (aka the Uninstallation 14) is pure â– â– â– â– â– â– â– â– , especially for the beginners.
For some skills, yes, lvl v is basically mandatory. Advanced Weapon Upgrades, and pretty much all of the fitting skills, benefit greatly from that extra level.
Weapon specialisations, not so much. You can leave those at III or IV for quite a while.
Then there’s skills that are great on a specialised alt, but you might not train on your main. Freighter and Mining skills for example.
Some skills really shine at V. The scanning supports come to mind. At V, you can use the T2 arrays, which are a significant upgrade on T1.
Alot of V skills are just to squeeze out the last drops of DPS/Yield etc.
Some lv 5s make QOL better. Some lv 5s are really just for the vets. (Like weapons spec V)
I have spec level 4 in many skills, but I wouldn’t bother with level 5 unless you use a weapon often and have nothing better to train.
The other advice is generally good.
The only thing I will add is: if you’re training capital ships, the extra % from going 4 to 5 is often absolutely worth it because of the cost of the hull. For example, going from 4 to 5 in a capital weapon specialization skill is still merely 2%, but it is “merely” 2% of a very large DPS number. So that 2% can translate to a number that is very large.
For weapon specializations, it is worth it when you use the weapon or ship type very often, Gerard Amatin is right on the money.
Admittedly this is me speaking from the perspective of a fairly old character, but if you stick around long term in Eve, and having topped 5 other skills, the level 5 specializations start to look quite attractive, even more so if you have clone with +5 Learning skills on all 5 sections and cerebral accelerators at hand when they become available, those long training times can come around quite shortened. 
And also to reiterate what others say, once you reach a point of having trained everything vital and having nothing better to train… why not go for the Level V? ;D
I have only recently hit small weapons spec 5 across the board. I have medium weapons spec at 4 and large weapons spec at 0 in the queue. As you can guess I mostly fly BC and smaller. 18 character years, but I havent been specializing in combat
Pyfa the skill 5, see if you think so is good place to start. Some skills I’d have worth the 5. Others, not so much. To my eyes anyway.
I have fitting related 5’s as mandatory in time. It can pull a cpu/pg rig/mod best case. But I’d put 5 when more “done” basic goals. Also put in dream fits/ships for later. even 5’d out you may find you need fitting rigs anyway. But if it get that to t1 rigs not t2…that saves isk. Especially if pvp an interest.
PVe…are you a slave to isk/hour? If no…well then optional (unless a module needs it ofc). If being there 1 extra minute is not a deal breaker and other skills need work go with that.
PVP…yeah. if doing what are you doing. Some recent deaths…well when 12 people lock you you get dropped. skill level 4 or 5 death will come.
It depends on your activity and the skill .
Sometimes a V skill can enable a fit, including weapon specializations.
It depends on what you do (pve, pvp) and what you are facing
and also maybe lvl 5 insted of lvl 4 for one skill seems to be a tiny gain. But when you add several skills and several tiny gains, it results in a significant gain, so…
Nah, depending on how new you are Lv. 4 or sometimes 3 is fine. You’ll thank yourself for prioritizing Advanced/Weapon Upgrades, and the CPU and Powergrid management (fitting). As you look at fits you’ll find some commonly used modules that require level 5 for skills (looking at you, Hull Upgrades). So if you’re still new, only train level 5 on stuff you need for unlocking things.
As you get more experienced your tastes will probably change. Once you have tried several ships then you can think about topping off your specialization skills for your favorite rides. I know I love me some artillery spec 5. By then you’ll think “oh I also need my speed skills, and I should top off my shield skills, etc.”
To TLDR this thread.
“It depends”
level IV magic 14 is more than enough for the beginner and some of them are already trained that high
Level 5 ship skills are pretty solid, as well as the ship class skill for T2 and subsystem skills for T3 hulls.
For example, Hecate going from level 4 to level 5 in Gallente Tactical Destroyer will provide additional 5800 point of damage while overheating during the lifecycle of your blasters (and better tracking too).
2 or 3 per-level bonuses on some ship attributes really helps. Look at Logistics Cruisers.
T3, level V everything is critical, especially cruisers and subsystems.
recons, logistics, marauders, orca/porpoise, you can get away with IV but they are so much better with V and some uses of recons and marauders wont work with IV.
Some HACs are ok with IV but absolutely insane with V - missile muninn is like that
Weapon Specialization V is nice to have but not necessary.
Weapon Skill V, on the other hand is almost mandatory, for the weapon classes you actually use.
Shooting Rockets ~8% faster certainly is nice (Rocket Specialization I → Rocket Specialization V), but what you really want/need is the ability to use Rage and Precision munitions (Rocket Launchers V and Rocket Launcher Specialization I).
The T2 Launcher itself also requires the non-specialization skill at level 5, so unless you have the weapon skill fully skilled, you can’t use faction or t1 munitions with a T2 launcher instead, either, but need a meta launcher, too… which means you might simply not be able to use a fit at all, not even with different ammo.
I do intend to level 5 weapons skills, eventually.
Just that waiting 60-80+ days to level 5 2-3 skills when I could be doing things (mainly sub-cap PVP) at level 4 in the mean time is a long time to wait.
It’s absolutely necessary if you aim to fly T3 crusaders, and it can certainly be very useful in the long run if you want to boost a mining fleet with an orca.