I have a 3 year old classical guitar that I bought for around $500. It has a truss rod, so I was just wondering: is it worth putting in for a basic setup? Can anyone tell me if guitar repairers do anything to make the sound and play ability of classical guitars better. The action is a bit high for my liking currently but if they can only lower the action but adjusting the truss rod would it be worth putting in?
It's not just about making the action higher or lower...it's also about getting the proper relief in the neck. The neck of a guitar isn't ruler-straight: it bends upward in a very slight gradual curve from the body to the headstock. If that curve is too flat you'll get pernicious buzzing, and if it's too fat you'll have strings too high and possibly slight intonation anomalies. The neck relief is set by the truss rod, and the action height is set by the bridge and nut height (and also the truss rod).
A setup will cost in the neighborhood of USD $75-$100 and will likely include a bit of fret dressing...all increasing the playability of the instrument. Whether that's "worth it" or not depends on whether you're better served taking that $100 and putting it toward a higher-end instrument. Sometimes $300 instruments are absolute gems, sometimes they're total dogs...impossible to tell from a stackExchange post which you have.
If you're unhappy with the sound and playability that you're getting, it's definitely worth taking your guitar in for maintenance. Most guitars usually benefit from having a setup done at a guitar shop. Very few guitars come out of the factory with great playability. You should be able to get the action lowered and thus enjoy your guitar more. That extra enjoyment and improved playability would make it worth your while.