Forgive me if this seems like a dumb question.

I am morphing into the roadie I've always wanted to be. I ride a decent MTB for commuting and have also used a hybrid and a road bike modded with flat bars for same in past. I defintely prefer the road bike geometry.

I want to get a decent bike and do some long club rides, eventually a century and maybe a few short credit card tours. I MAY even try a snail race or two (I'm 41).

I recently picked up a used Trek ('86 Tri Series, Reynolds 531) and so far I love it. There are some fit issues (it's an 18" - I like the SO height but the 3cm TT is a bit short for me. I'm 5'8", 29" inseam)

I have been lusting after high end bikes for some time so I know I'll get a good one eventually. I bought a 'cheapo' (the trek was $200 on CL) just to test the drop bar waters first and get some ideas on frame size, etc. I had planned to maybe buy a new steel bike (Bianchi, Lemond, etc) for years in the $750-1500 range but now I figured why not cut to the chase and get a nice TI bike, something I can just use and grow with instead of flipping for another bke in another year or two. I don't 'need' a top-of-the-line racer but I do want someting that makes me smile and I have a cruddy bike or two already, so that's not an issue here.

My problem is I am still wary of dropping $3-4K on a road bike until I know more about what I want/need. I know lots of test rides at shops are in order, but I'd like an interim bike, someting between my trek and the 'new' baby, but I'd like to pay less for the interim bike in case I goof on fit, etc.

Asssuming I am buying a 'nice' bike (race quality, say Dura Ace, selling new for $3000ish and up), what sort of prices should I expect to pay? Obviously condition matters, but assuming a bike has been used but not crashed, scratches but no dings, cosmetic stuff only, a few years old (5 max), no crazy mods, etc., is there a percentage of the original price you would not go beyond? Ie, is 50% of original price too much to pay for a gently used bike?

In the past it had seemed to me road bikes retained their value better than mtbs, due presumably to the uber-fast marketing of new & improved mtb doo-dads. The Road bike world certainly seems to have picked up on that, so not sure if that is a good thing for a used road bike bargain hunter in today's market......

any thoughts?