Thanks for the ping @Shipwreck_Jones 
Co-Head of the United Standings Improvement Agency [USIA] here. For 12 years now we’ve hired mission runners to service our clients. Here’s how most of our veteran runners view this topic:
- First, an important correction to what Anderson said: the faction loss is actually -0.001 rather than -0.01 (just checked on Sisi to be sure). That extra zero makes a HUGE difference, believe me. For all intents and purposes, these standing losses are negligible relative to the gains from storyline missions that can be used to repair these losses.
- Do note, however, that the -0.001 loss also applies to friendly factions as well, so if you incur the decline penalty with Gallente, for example, you would end up incurring the same penalty with Minmatar, Sisters of EVE, and a few other factions. Not terrible, but still worth mentioning. So the net loss across all factions could be closer to -0.01, but not for an individual faction.
- Many veteran runners are more than happy to incur the decline penalty repeatedly because they feel the gains far outweigh the losses. This is particularly true if
- (Good) agent availability is limited (eg. with pirate factions)
- You are chain-running burners, esp. in nullsec where literally more than half of missions offered are burners, so you want to skip non-burners in favor of burners
- You plan on running awarded storylines, thereby gaining more from the storylines than you’ve lost via decline penalties
- You work for USIA, in which case you are paid by performance and you know that accepting shitty missions or wasting time changing agents can cost you more in salary than the standings penalty is worth
- You want to skip missions known to incur megahits to faction standing (eg. -0.4 for destroying repair depot missions) and would rather incur the far lighter -0.001 penalties instead.
- As Anderson said, if your faction is comfortably above a certain threshold, then your faction standings will enable mission access even if your corp standings drop below the requirements.
- etc
I should note that it is not always practical to have faction standing determine mission level access (for high level missions at least), particularly if you want to be able to mission for multiple factions at the same time. It is possible to raise and maintain all factions above -2 (and even above 0) to maintain access to all mission levels with all factions at all times (I will not go into how this is done here); however, it is too impractical and in some cases impossible to maintain sufficiently high standings with a one or a select few of these factions to have to serve in place of corp standings for determining mission level access if you are also trying to maintain the rest of the factions above -2. If you find it to be too impractical or outright impossible, then you need to carefully monitor your corp standings after every decline to make sure you don’t drop below the threshold needed to access a certain mission level.
Would EVE benefit from decreasing the decline penalty window? I can’t say for certain, but I do think that EVE’s standings mechanics need to be re-evaluated from the ground up. Among other things, if the -2 threshold (which we here at USIA call The Deathline™) were removed altogether, this thread probably wouldn’t even have started. There’s a good argument for removal, too: EVE is one of the few games in existence where a brand new character can enter the highest level content (eg. incursions, 10/10s, high-class WH sites, abyssals, etc) from the moment of creation (regardless of ability to ‘engage well’), and missions are literally the only content in EVE where this is not possible, and there’s no good reason for this exception to exist. Why should players be forced to grind low level content just to get to high-level content? This isn’t required for any other content, so why should it be required for missions?