we're always tinkering with our bikes, no? what are the best changes you made to your rides that have improved both your race or training performances? i'll go first:
1) a pair of Dugast Typhoons in 32c. maybe it's just placebo but this rubber is so far better than any other tubulars that i've tried (Vittoria Cross Evo XGs, Challenge Grifos) it's not funny. So much so they should actually be illegal.
2) 1cm shorter stem. before the road bike and the cx bike were set up identically for position. but now with the shorter stem it makes a huge difference. no joke what an improvement it has made in being able to stay upright and move the center of gravity back over the rear wheel.
for me, early on, the best upgrade was replacing a notched-tilt seatpost with a two bolt design. it never fails - a botched remount by my 160 pounds in a race situation will force a notched seatpost to point my saddle straight up, making continuing uncomfortable at best, and impossible at worst.
and the two bolts IMHO should be front and back, not on both sides.
A set of last year's model Easton EC 90 SLX wheels paired up with FMB 34c SCC Sprint (file tread) tubs. Dropped 3/4 of a lb from my other SS tubular wheelset. These things spin up so fast and the tires stick so well to our SoCal hardpack and grass.
Also swapped out my steel fork for an Alpha Q, which I like a lot (helped bring my bike to under 16lbs), but the wheelset is the big upgrade.
As far a bike fit, I swapped out for a longer and lower (-17 degrees) stem, bringing me closer to my road setup. Seems counter to most advice but I have long arms and torso and am able to deliver more power and carve the turns better in a lower position.
Like many others, my best change this year was upgrading my wheels to tubular fangos from from tubeless bulldogs. Low pressures and good grip have made me more confident in the corners and I haven't wiped out in a corner yet.
I also upgraded my 105 shifters and rear der. to 7800 dura ace I got on close-out. I'm not as good at shifting before a corner as I should be and the dura ace lets me shift in the corner when I need to. Much better than the 105.
I wouldn't totally give up on tubeless. I think my problem was with my choice of tubeless tires. I didn't like the bulldogs, they wore down quickly and didn't seem to hold the corners as well as others. To do it again, I would probably go with the Michelin Mud's tubeless, I ride with quite a few guys who have had luck with that combination. They still burp occasionally when hitting roots or buried rocks, but I think they grip a little better in the corners than the bulldogs.
I was also able to get a deal on my easton ea70x tubular wheels that was too good to pass up, I think they were around $250 on chainlove last fall. It doesn't have to be all that expensive.