I don't really have a good answer for that question and it is a good question. When you say your store them properly, I assume they are in a paper sleeve or something comparable?
I've found that if I play a record before cleaning it and then play it again after cleaning it, the quality is markedly improved but I am not certain how long before I'd have to clean the same record again.
The kit comes with a couple of bottles of the cleaning fluid. You anchor the record on the machine and then turn the motor on. After applying the fluid, you take the brush that comes with it and basically "scrub" the liquid into the grooves really well. Then you put the arm over the record and the vacuum sucks up all the fluid and the dirt along with it. The fluid is captured in a tube that has a crimping tool to keep it from leaking out. After a while you need to drain the tube and you can see all the crap that was in the grooves. I was amazed. I find that I will generally clean them before playing them and then if I know that I've done it recently, I let it go until I can tell a difference.
A couple of cautions: You'll need to be careful not to let the liquid get on the labels. Also, the anchor mechanism that holds the record to the plate and the vacuum arm that comes with the machine is designed for 33 LP's. If you are using it for 45's, you need to purchase a separate anchor and vacuum arm to accomodiate it. VPI sells the the 45 adapter kit and the fluids on their website. If you go on VPI's website, you'll also see the pinnacle of turntables! They are amazing.
http://www.vpiindustries.com/main_tables.htmI believe they are really worth it if you are into vinyl.
When I bought the machine I called my mom and told her about it and her response was "you realize that your dad used a tee shirt and rubbing alchol don't you?" I answered it was only because he didn't know about this machine!