Ive got two more little points to add to whats been said, firstly, about the defence of systems:
yeah, it probably would be a lot harder but bear two things in mind, a) its ridiculously easy at the moment to completely surround the exit to the jump path/s with gaus guns, it almost goes without saying that youre going to jump into the guns when youre attacking so obviously you'll be packing enough to get rid of them anyway (theyre almost pointless if you see what i mean). b) if youve got say 6 planets in a system, youre also going to have 6 times the ships and defences as you currently do defending one planet, so its all relative really.
Secondly in regards to the jump paths, (it would probably be better to make a seperate thread on this because it amounts to a big change but...) i was trying to think of ways in which your fleets could feel more like actual fleets and less like regular rts-control groups. (I dont think I explained that very well but hopefully youll understand what i mean)
What i came up with is how about you only give capital ships jump drives, but sort of area of effect jump drives. The idea being that if i want to move ships from one star system to another, i HAVE to have a capital ship in that fleet that can open the gate for all the other ships. Btw Im goiing with the idea of getting rid of the jump pathways! sorry i didnt mention that.
right if youre still following all this what we now hopefully would end up with, is that if you want to stage an attack on a planet outside your solar system you actually have to put a lot of resources into it, AT LEAST one capital ship. Hopefully you can see the advantages of this, you dont get the whack a mole defence because the minimum force they could do this with is a cap ship, which if on its own, is a vulnerable, expensive way to try and harass someone (making it risky instead of annoying) and if its escorted by a big fleet makes interstellar combat more fun

because as everyone knows, big fleet-on-fleet engagements are ace! And if youre still upset about the possibilty of whack-a-mole, just put a 5 minute cooldown on the drives, after all you need to jump less often if you dont have to make 6 jumps to get from point a to point b. And finally my hope is that your fleets would feel a little more autonmous, more like expeditionary forces than just a bunch of units you drag selected and told to move to the next planet.
any thoughts after that massive rant?

EDIT: also i totally agree with what Rhaw said about sensors! It's a bit sad at the moment that once ive arrived in a system I immediately know everything thats in it

it seems to me it would be a lot more strategically interesting and therefore, fun if you could hide ships behind asteriods, moons, planets etc.