But that's exactly what reserves are for. They are a cheap way to raise your military potential. With the buildup of forces in the 19th century, drawing on reserves (there really are two types, the game only portrays one) was the only way for many countries to keep up with their neighbours (who would then again increase their forces etc.).
By this time, reserve units also weren't universally low quality. Generally you'd distinguish between different types of reserves, 1st Line, 2nd Line, Lines of Communications and probably internal garrisons, policing etc. The 1st Line units would not be much worse then regulars and as war progressed even the 2nd Line would become valuable combat troops. I'm not sure how experience works in game terms, but if it has an effect on combat as I hope that will play the correct role. Regular units will accumulate experience over the years (fighting in small wars, against insurgents etc.) and have a slight edge over reserves once mobilized (as all reserves start at 0 experience).
One last note. Reserves are cheap to create, but expensive to mobilize. You will take a serious economic hit when your craftsmen and clerks are drawn into service. While their conversion to workers and famers is probably a bug (well it doesn't quite look like a bug to me, rather something that would take up expensive space in the save game files) in 1.03, it's neverless a very painful factor once you demobilize and have to rebuild your industries.
Marc aka Caran...