Hi Chriss,
I am a Nikon follower, so not well up on Canon's range, Colin will no doubt advise.
In general, if the lens has had an optical re-design, or even just an upgrade of multi-coatings and/or addition of IS in the intervening 19 years, I would expect that a more modern lens would be better. But it is easy for me to spend your money.
So I ought to add that only if you are confident in your PP skills that you are getting the best sharpening possible should you consider buying new.
If 1991 was the first release date for the lens design, I don't know how old your lens is, or what kind of a life it has had since new.
I really cannot judge sharpness on such a small photo, I do not even know if it is the full frame reduced to 500px × 317px, a crop of 500px × 317px from the centre of an unsharpened picture (which I doubt), or the flickr re-sized medium jpg of one of the aforementioned.
I don't think that was much help, sorry,
Colin, I guess that's why its not sharp because I didn't apply anything on PP. blah
(Going to read CIC sharping tut, brb)
You might find this handy ...
When/How to Best Sharpen a Digital Photograph
oh great another adobe book i can use to spend money on thanks she said sarcastically