I'm in the middle of my build (well, actually going backwards but the good news is that the fuselage damage from the lift failure wasn't too bad and so I only have to redo three skins and the doublers aft of the spar), and love everything I'm putting into it. But, if I were to do another, I would change a few things, starting with honoring the KISS rule. No A/C, no built-in O2, no overhead console. A simpler panel, without Vertical Power. No rudder trim (no yaw servo in current build). I'd forego an interior, especially a headliner, in favor of sand and paint.
I'd still do electronic ignition and fuel injection, and keep the throttle quadrant. Also keep AOA instead of the stall warning system. I'd also keep the center console, which is a great place to connect headsets so you don't trip over cords as you get in. Everybody talks about the third door latch but my doors (c. 2008) are so stiff it takes real effort to twist them enough to only latch either fore or aft, not both. Maybe later kit doors are more flexible, so I won't discourage that. However, I like the aftermarket ends for the door latch tubes. I also added platenuts to the door hinges to make them easier to work with, which is a mod I heard about here on VAF and is a great idea. Also, the trimming of the blocks in the front seat rails so the seats can be removed. And I like the extended handles for the seat backs.
A friend machined an insert for the step tubes, so you can put a bolt through them and there is more bearing surface for the bolts to make them more secure. It is also worthwhile to get a machinist to drill the holes for your axle nuts, though reaming the holes to mate the gear legs to the towers was no problem on my own. Getting flex lines for the brake system is much better than the aluminum tubes down the gear legs and around the rudder pedals.
In the engine compartment, I highly recommend a Wolf remote oil filter and that big engine should have enough power to run a backup alternator. Forget the flyweight starter unless you like replacing them all the time; get one that's up to the task. And no internally regulated alternators; I am convinced that the regulators can't take the heat in the engine compartment. Speaking of the heat, I'd insulate the tunnel and add access panels for the fuel pump and filter.
Not that I'm opinionated or anything.
I'm enjoying my over-the-top build but I'd also like a simple -10 to replace my -6A. You'll have to decide how to balance building/flying for yourself.
@Thad: NAV? What's that? Seriously, you need to decide how important VOR navigation is to you anymore. It's not a big deal to put a V antenna in the vertical, which is the best option if you expect to navigate with VOR in IFR. Otherwise, if it's just a backup for GPS and VFR, than the archer antenna should be fine. I've had no problem with one in the wingtip of my -6A, but with my plan to have an all-the-way IFR panel for the -10, I went with the V antenna there.