I Agree...
I agree with LittleDog... If the Radio Shack Mic is fitting your needs, and you're happy with the sound you're getting, I wouldn't be too upset at continuing to use it...
You need to ask YOURSELF - Is my vocal the way I want it? Does it sit in the mix like I'd like it to be... If not, then maybe a different mic or some other adjustments would help it work - Or maybe you need to look at a new mic...
When I first started - I used an old EV PL25 or something like that... I thought is sounded great and someone told me to go get an SM58 and that would "Solve it all"... Well, it didn't - I still used the PL for quite some time...
A few good low cost mics that I use are: Rode NT1, SM57, SM58, Rode NT3...
Maybe try going to a low cost condenser mic... Those may boost your signal and give you a little more control over your recordings...
Here's a good example - You're using your RS mic for recording one day and you get some good vocals but you need to finish up the next day. The following day you re-record some parts and finish the recording... Upon playback of some of those vocals you find that they "sound different" than the ones recorded the day earlier. It could be because when you recorded you were standing six inches closer the day before or perhaps you were at a different angle...
Buying a more expensive mic generally means that this kind of little detail / change is erased... I've found that with the NT1 I can have my clients stand at any position with 24 inches of the mic - on the side - standing direct, etc. the the "tone" of the vocal will be the same...
I've read a number of books and experimented with lots of stuff and have come to the realization that: "More expensive gear only means that you can make more mistakes in your technique when recording or mixing..." (remember this is a "general" statement) ie: because the mixer has such great signal to noise ratio, you can leave a few sliders up. Or your vocal is not placed "exactly" at 6" from the mic but the mic picks up good enough to compensate for that.... That's what professional gear will do for you...
Bottom Line:
Use your ears and if you like what you hear, continue using it...
If it's giving you trouble or there's a detail you don't like? Get rid of it!
Riverdog
www.homepage.mac.com/riverdog