Comments from a Velocity owner and aeronautical engineer who also
didn't have time to build, so bought instead. Additional comment is
that my Dad has a Mooney 201 that I've flown quite a bit so I think
I'm fairly well placed to at least comment on your question.

For me, there were a few big drivers for the Velocity.
1) Stall characteristics - I can pull the throttle, slow to stall
speed, roll into a 45 degree bank and pull the stick to my stomach and
nothing happens. I know this isn't an issue for "good" pilots, but
the records are littered with stall/spins. I'm human and make
mistakes. Whether rational or not, the stall/spin is one of my
biggest fears.
2) Maintenance / avionics - with a homebuilt, I can do everything
myself outside of the "annual". This has helped with the nuisance
issues, but I still use the local A&P for a lot of work.
Additionally, I have access to cutting edge development that is too
expensive or simply not available to certified aircraft. Example is
my Trutrak 2 axis autopilot / ADI. I absolutely love it and my Dad
can't put it in his Mooney without a LOT of effort if at all.
3) Factory support / aircraft complexity - factory support may not be
as good as Mooney, but in the experimental world the ability to get
factory check out and factory annual is a big deal. Also note that
the Velocity can perform extremely well as a VERY simple airplane. My
plane is fixed prop, fixed gear and keeps us with a 201. My plane is
more basic from a maintenance perspective than a Cessna 172 and was it
a simple transition from that plane.
4) Useful load - I can put myself, my wife, both kids, the dog and a
weekends worth of luggage into it and still easily cover 300-400
miles.

Jeff