To make Abyssal sites more dangerous while more rewarding I suggest that Ramping up of Abyssal Sites takes place.
A Ramped Up Abyssal Site would be a special filament for any of the normal sites that could be obtained from exploration sites or level 5 Abyssal sites. The difference in a Ramped Up site compared to a normal site is that a Tier I Ramped Abyssal could be a Tier I to a Tier III. A Tier II could be a Tier III - IV, Tier III a Tier I, III or IV, Tier IV a Tier II, IV or V and a Tier V could be any Tier from I to V.
The Ramped Up Tier would be listed as Dark, Electric, etc. and would fall within a known Abyssal site type.
The rewards for a Ramped Up Abyssal site would be approximately double its non-ramped up version while having more towers and slightly stronger NPC’s to deal with.