I used to stash away a consecutive run of clean UNC notes and then spend them as the need arose-- often not discovering if they were rare or not. As a 16 year old working at a car wash, I only found a couple radars, 1 decent $2 replacement and 1/2 dozen crappy ones (73 $1.00), and I stashed 54 $20 as they disappeared from circulation.
My point is-- I had a pretty mediocre collection which I carried around with me before there was a Charlton-- but I was happy since the collection only cost me face value. Then I bought a 1937 AU $5.00 $20 VF DF, some crisp consecutive $5.00 and little by little started adding to my collection (from age 18 - 25). I guess a lot of the money I stashed was wasted (in that it could have bought me something). But I often brought my old ratty bills to collectors who had stands in the malls, and would trade them in for better notes. I just hope they weren't test notes because I was unaware of the S/R or G/R significance!~ (most dealers wouldn't give anything above face, but would be happy to discount the one he was selling- or charge no tax). I put the collection on the back burner while I travelled, and was busy with other preoccupations.
About 3 years ago-- I began to renew my interest and started the stash and save technique once again. I don't think its such a good way to collect unless you know you're stashing something collectible. I realized as I researched here, and elsewhere that I wasn't getting much "bang for my buck"
So I've tried to take whatever I stash and turn it into something worthwhile. I also sold almost all my notes from my childhood, and converted the money into upgrades. I've been on steady uphill pursuit of superior notes. Its what I encourage all collectors to do. It seems a natural evolution of collecting (to want better and better notes-- as Oli1001 suggests).
My advice to anyone who cares to take it: if you got notes stashed away-- and you've got no reason to believe they're worth anything-- then get rid of them! QUICK! Go to your nearest dealer-- or a show-- or on eBay-- sell them and put the money back into something rare or desirable. Try to tie up as little money as possible unless you see it as an investment opportunity. You may want to buy up many of one kind of note-- if you think its undervalued and due to go up. Then (as rachelprivates suggests) sell. Buy and selling is a very good practice for any collector who wants to make something of his/her collection.
There's nothing wrong with selling portions of your collection off-- esp if the need is great, and the timing is right. The only problem is deciding what to sell, and how much. Lets face it: a lot of us love this hobby because we know we're into for the long term, and that it can pay us back- if the need is there!