I was thinking about doing this same thing for my personal system. The pressure drops for a coil range from .23 to .45. That is a huge restriction that wouldn't be tolorated in any heating only system. In my area heating is usefuly for about 30% of the year and cooling for about 15%. With that split I see a the chance to have some savings. Maybe only $15 a year though. More if they system is used in ventilation mode. Less wear an tear is another area for savings. This is something I can do myself. For you the cost to have it done might not be recouped. More siginfant for you would be to make sure you have enough filter area and proper ducting. Those you will definatly see the return on investment.
Dan
If you don't notice, I'm doing my job.