Going to disagree with most here. At your increased age since you last rode the Colnago- you have lost a lot of fitness. That Colnago bike is old with old components that although they may have been top-notch 20 years ago- Will not cut it up against modern bikes.
In the last two years I have gone from a Starter bike- Giant OCR- To a top notch Bike- Boreas Ignis and got a Respectable bike in a Giant TCR. The Boreas is a dream to ride- but the TCR is not far behind. So I reckon that you can get a bike that is easier to ride- lighter to ride and with better Modern components than the 20 year old bike you are considering buying back. With $1500 you are getting into the realms of a bike that is going to encourage you to use it.
May be sacrilege to say it- but Your Colnago is an old bike- A lot has changed in the last 20 years and it has not all been bad.
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How long was I in the army? Five foot seven.
Spike Milligan