Are you stupid? No. Are you wasting a lot of potential? Yep.
The advantages of UA: 1k will get you (for the time being) 3 int'l round trip upgrades from even the lowest of fares (the famed 1k Systemwides). You'll also enjoy 80-100% first class upgrades on continental US flights using certs.
See Premex's
The Unofficial United Help Desk for the insider's scoop on being elite on UA.
OTOH, the last thing I need is another 1k to compete for upgrades with

.
As for why you ought to switch from BA, isn't that obvious??? It's
British