Before spending any money, pop off a few cap rails and inspect down the sidewall of the pool in several places. If you have any corrosion, it may not be worth it to put good many oafter bad. While I think you'll be ok, it never hurts to check before you order up a $400 liner.
I agree to consider replacing the filter intake and possibly the return outlet if they are worn, or give you the impression they may fail. However, I replaced both of these on my old pool and while a "pain" in so much as you have to drain the water down past these to replace, it wasn't difficult to do, and didn't have any problems with the liner.
Also, you may have a problem with the cap rail screws. They love to oxidize and get stuck. It can be a pain to get these off without stripping or tearing the heads. Maybe scope out a source for new fasterners, some Wd40 and good screwdrivers.