I have the same problem with the mini dump and general system failure. no lag yet, but im still on my first game with entrenchment and havent gotten to max fleet yet. still, running dual intel 2.50 Ghz processors, dual 8800 512Mb graphics cards, 4 Gbs ram and no worries so far.
my only problem is with mines, i like them when they work for me, but seriously, i just scouted a normal difficulty AI system, and it was all yellow, just mines everywhere, i would spend hundreds of thousands of credits and hours of time just to spam enough scouts to clear even a portion of the mines in that system...
one thing i have noticed however, is that vasari mines are invulnerable most of the time, however ive noticed they 'decloak' their phasic sheilding at some times... though i cant tell when, ive tested with one of every kind of ship in-system, including scouts, and i cant tell why they decloak... it could be a range thing, but then u have to move your scouts close to every mine in system and if it gets destroyed you have to send another... if you are trying to clear mines in a system u annexed from your enemy, its hard enough, but trying to do that in combat situations is damn near impossible.
i REALLY think a mine sweeper is needed. some people put the flak frigate forward as a candidate... considering that the FF is pretty much useless now anyway (though, in all fairness, it has a higher average damage output than a light frigate or even a long range frigate....) i think that, or the heavy cruiser. makes sense in my opinion.
speaking of which, i think it would make more sense if they merged the functionality of the garda with the percheron. i.e. keep the percheron but simply mount the garda's flak cannons on the carrier cruiser. that wipes one useless ship off the map and makes percherons a lil more useful in fleet actions
im just running ideas here though