I went the same route, CNA to RN. For me, totally worth it!
I guess I don't remember being bothered by the physical aspect of being a CNA, I will say I was in much better shape and a lot less fluffy when I was CNA than I am now. I'm also was lucky that my CNA instructor really reinforced the importance of proper body mechanics, so to this day I am very conscientious about that. Not that some days I'm not tired and achy, but I figure that is par for the job. I also enjoy caring for others, so this outweighs any physical discomfort I may experience.
In fact, I think it has made me a better nurse. Not only am I competent and comfortable performing many of the same tasks I performed as a CNA (positioning, transfers, ADLs etc) but I often "sneak" in my nursing assessments during patient care. I think it also contributed to being able to build a better rapport w/ my CNA's when I worked at a SNF and allows me to assist the CNA's I currently work with in hospice.
Having said all that though, you will have to figure out if this is what YOU want to do. Good luck in whatever you decide:)