Hum... lots of interesting thoughts here... I too don't race, but I do have a somewhat restricted amount of time for riding, and I want to get the most out of that time.
I'm riding a sort of heavy hybrid now, but was planning to upgrade to something nice as a reward for getting under 200 lbs. (or maybe just 207 - 'no longer obese' point for me) - now I'm thinking that I'll keep pushing the hybrid around at least weekdays - not so much to increase speed as to make the workout just a bit harder - but, someone earlier said 'that's not good training technique' - why is that? Whats the context?