The 97 CR250 wasn't a real good bike though was it? Too stiff, I believe (not that I've ever ridden one).
Adding HP and weight to a bike that doesn't handle nice will never make it better... The alloy framed CRs didn't really start to work 'properly' until 2001 or so, IIRC - maybe your 500 engine in a later 250 frame would give a different impression?
The KX500s got PVs in the mid~late 1980s. I thought that all of the 500 2-strokes were seriously detuned/under-developed, so that mortals can ride 'em... I have enough trouble hanging off the back of my Husky WR360...