If you have been shooting trap for a couple of years, you know what chokes you need for your style. If your barrels all have the correct fixed chokes, AND you are happy with the pattern performance, why change?
If you are not happy with the performance, how do you know changing to choke tubes will help? It may well be something, or a combination of somethings else.
Personally, I'm tired of sneaking up on a solution. Try this, then that, and maybe finally fix it. When I bought my last set of Perazzi barrels, two of them didn't pattern as well as I've come to expect from my other Perazzi barrels. So instead of dinking around, I sent them to Kerry Allor (my current fav for outstanding performance and on-time delivery) and asked him to fix them. They now pattern beautifully, shoot to the same POI, and have the smoothest bores and chokes I have ever seen.
Personally, If I were going to have choke tubes installed, I'd send it to Allor or your favorite barrel smith and have them install them. Then you will be certain they are concentric, the lead-in is correct, and the performance is there. I have become very leery of people who do barrel/choke/forcing cone work and don't test the results before they return them. I'd rather pay a small amount extra to have my "smith" test his work and guarantee the results.
I guess the moral to this story is...If it ain't broke, don't fix it. If it is broke, don't take halfway measures. Give it to someone who will fix it correctly the first time, tests his work, and proves to you it does what you asked. Then you will be happy, and resale value will not be diminished. It may well be enhanced.