If you do decide to change, you may have to upgrade your grouppo, depending on what you have exactly.

Most triple-compatible shifters will work with a compact just fine. In fact, with indexed shifting, you can set it up so that you can do a half-shift, to give you less FD rub. It depends on what you've got. You will need a short cage, double (or compact specific--but not necessary) front derailleur, and depending on what you have and what you move to, you may need new shifters.

So if you get new shifters, can you find some more 9-spd that will work? 9-spd is getting phased out for a lot of levels, so say you have old 9-spd Ultegra. Well, you can't find 9spd ultegra components anymore, so that means you'll have to overhaul your entire grouppo to get the right shifter for your new FD. If you have a newer, lower level group, then you might be able to change your shifters and be done with it. These aren't really cheap, though, compared to the FD purchase. So if you want to change cranksets, which can also be expensive, you may want to just look at an entire group upgrade, which can be bought as a unit for cheaper than doing it piecemeal.

Depending on your cassette range, I wouldn't discount the ease of the 50 (or 48) over a 52 or 53 big ring. Do you use the easiest cog with your easiest ring often? If not, then you might be able to find a good cassette range that will work with a 50/34 to give you a pretty useable low end while also making that 50 a lot easier to use than your current cassette with a 53. You may find you have more useable gears with a total overhaul of your gearing.

To figure that out, you need to look at what gears you really need on your current setup, play with a gear inches calculator and different crankset and cassette sizes to see if you could move to a compact. I wouldn't worry about never using the big ring too much. However, if you like to use your full cassette with your middle ring, you're going to be cross-chaining a lot and wearing out your chain unnecessarily when you could potentially build a better setup.