Not to mention that extensively modding smaller ships seems to be more rewarding than it is with larger ones.
Or maybe it's just me.
i don't think it is just you. for me, i like about modding that it an tackle the "weaknesses" of a ship as well as playing it strength. my DBE now is as fast as a DBS without modding - so i fly it most of the time ingame in 2.1.
for exploration, it opens up for a lot of ships, engineering "your" special exploration ship - and when it is a ship unusual for exploration, it gets an exploration vessel via the upgrades. at least as long as we all remember how it is to fly an unmodded ship ;-)