The upgrade is simple and relatively cheap - a $5 spring plus the BA/G250 service kit. But I dive both the R109 adjustables and the R156 Balanced Adjustables and find little to no difference between them. In fact, I always use R109s in conditions with strong currents as they have less likely to suffer from current induced free flows. Both breath almost as well as my wife's S600. You may be experiencing a problem with your R109 that may not be corrected with the upgrade. I remember reading somewhere (probably on this board) that manufacturing tolerances has changed over the years and, although design compatible, some older metal regs may not accept and work adequately with modern parts. Although with about a dozen scubapro metal 2nd in my arsenal, I have never had any problem.
I suggest you work on that R109 before trying to cure poor performance with the BA upgrade. Or at least wait until DAaquamaster chimes in.