I've made it to wave 9 myself as the NR but then got toasted, bummer because I had just got a random drop for 2000 credits that could have put me back in the game if I had survived.
It's actually quite a bit harder than I expected. Maybe guarantee a bonus after wave 5, 10, and 15? Or perhaps raising the credit income just slightly or 1 extra starting ship to reduce difficulty a little.
Perhaps consider adding heroes? Either as buyable, or a random drop. Could be cool.
The perimeter turrets cost way too much right now. I can't justify dropping 300 credits on a flimsy turret that is difficult to protect.
Idk if it's possible, but having buyable Golans, or random drop Golans could be cool too.
All in all, fantastic job on survival. It's unique and a lot of fun and requires definite strategy. Above are just some ideas to toss around.
EDIT: After doing some more playing, I discovered that the random "temporary attack boost" drop is broken. The description said it would last for a short time but it lasted at least 3 waves. Enemy hard points were going down in one shot as far as I could tell. On the Praetor wave (10), I looked away from my praetor attack group of fighters to deal with another angle and it was gone when I looked back, just seconds later. My fighters weren't all focused on it either.
If that boost lasted forever, I might have been able to get extremely far. Unfortunately, I wasn't expecting to survive that long and had to go to work.
But anyway, in terms of balance this should be fixed, it's just too good. The NR has survival the easiest imo, the BAC's are amazing, even better with the new fighter system since they still give you 4 at once.