I just bought a .22lr conversion kit for AR 15. Although I am not a big fan of conversions, I found this conversion kit to be a good addition to my needs - it will let me shoot with the exact same setup (sights, optics, weight, ...) as my HD setup, the kit does allow me shoot good ammo very cheap without wearing out BCG and being very soft on the barrel.
The unit I bought was a CMMG .22 kit, hopefully it will get here next week and I will give my impressions.
I kinda went the other way myself. Back when I had my Stag I was thinking of getting a conversion for it... After considering the costs and such, I ended up just getting a little .22lr instead. I was like you, I wanted the conversion kit so I could basically keep everything the same but shoot cheaper... But then it dawned on me... A marksman is a marksman NOT because of his equipment, but because of his skills... Those skills are honed by practice, and they really aren't equipment based. A true marksman can quickly adapt to any type of equipment, good or bad. At least that's what I convinced myself. I figured just getting another rifle was a lot cheaper than a kit, and it gave me the opportunity to send a lot of lead down range and work on my fundamentals... Trigger pull, breathing, etc...
As a matter a fact... I just stopped at a local shop last night and picked up a new remmy 597. I had sold the old Marlin I had to a friend that wanted to buy his first firearm, and frankly I missed it...
Got it stripped, cleaned, and lubed (my way) last night, as well as the scope mounted and bore sighted... Gonna take it out tonight and get it zeroed...
One thing that can be said... Conversion kit or stand alone rifle, there isn't much that can beat a .22lr for practice... It's practically a staple for any collection!