The main problem with trailers is drag. You feel like you are pulling something, and you work a little harder. Since the big advantage to running a tour on roads is low rolling resistance it kinda sucks to mess that up. However there are pros and cons to everything and the list of handling, parking, and price features, pretty much sways in both directions depending on your individual circumstances.
If we drive past a tourist with low riders my wife whispers "too much gear", but if you are bringing the kitchen sink it all has to go somewhere, and be easy to get out I don't think there si a right answer. If you already have quality racks on your bike, and you don't blow the bank on paniers, I think the potential is there for paniers to be a lot cheaper than the average BOB set-up. Of course most of the folks I see with a BOB have paniers also.
I think the logical thing to do is:
- Figure out how you want to tour, use hostels and motels, camp out, stealth camp. By yourslef, sharing gear with others, etc...
- Decide what gear is totaly essential for that style of touring
- Figure out how big a pile that is, and where it is going to go on your bike.
- Through that process determine whether paniers, trialers, or both will work best for you.