mid-level groupset

I think I Know what you mean about veloce, after many years of great service mine seems to require more frequent adjustment and I suspect a brand new professionally installed Athena or ultegra would be slightly more accurate in shifting.

However that's a big investment to make for something that would give marginal improvement

And going to 11S requires even more change

OTOH, everything wears our eventually, so possibly look at making sure chain and cogs are perfect order, replacing both at same time if necessary, then perhaps trading up the RD as an interim measure? Bikediscount.de had record and chorus 10s RD's very cheap recently

I have a similar stable to BTB but I prefer Campag. My experience of the shifting is that Shimano shifts up really nicely and the paddle shift to change up is simple, smooth and effective. My Shimano kit doesn't have the definite click of Campag and I find that shifting down can be a bit hit and miss and that I have to feel for it rather than just getting that Campag click and knowing that it has moved. I prefer Shimano shifting up and Campag shifting down. I much prefer Campag hoods but that might be just because I'm used to holding them ten hours a week.

I run both - campag on my commuter and shimano on my weekend bikes. All things being equal, I think I prefer shimano - but it's such a personal choice that you're best off trying it out.
I'd go for 10 speed - with the new 11 speed groups you should be able to get a bargain on 10sp.

Is everything clean, well lubricated and in good working order on the Veloce? I find mine works really smoothly. Another big difference to consider is the shape of the hoods. I much prefer my Campag hoods to my Shimano ones. It's worth taking a bike for a test spin to see how you feel on the Shimano hoods.