It's basically a tanking set, it's just been outclassed by later sets. Particularly, for STFs, the MACO shield alone gives similar resistance out of the box than the Aegis set bonus gives when it's fully ramped up.
Anyway, right now, though? Might actually be a worthwhile project. With the tribble test weekend being over, it looks like S7 will launch this week or next week at the latest, not leaving you much time to get another set before they become locked on the other side of the reputation grind.
Basicly the Aegis set is a shield tank set with a hull tanking proc, that is useful on ships that fight on the move. I have fleetmates who do elite STFs with the Aegis and do just fine.
I will say that the Borg and MACO sets are fairly easy to get and (maybe even in S7) cheaper than the Aegis.
If you have the ECs you can buy the complete sets on the exchange which is cheaper than buying the materials on the exchange. If you are buying it for Dilithium (via unreplicatable materials) it's ridiculously expensive (something like 50K+ Dilithium).
My Romulan Liberated Borg character made it to Level 30 and beat the (old) Defense of New Romulus with the skill point bug.