Side projects are for your enjoyment only. "To scratch an itch." as mentioned in "The Cathedral and the Bazaar".
If somebody else happens to use it too, that's all well and good. As long as you want to do it for yourself, then just go ahead and do it. Don't worry about anybody else. On the other hand, if you're not getting any enjoyment from it, then just stop. If the idea is good enough, somebody else will take over the reins.
Relevant phrases from "Linux is not Windows":
Increasing the number of end-users of proprietary software leads to a direct financial benefit to the company that makes it. This is simply not the case for FOSS: There is no direct benefit to any FOSS developer in increasing the userbase. Indirect benefits, yes: Personal pride; an increased potential for finding bugs; more likelihood of attracting new developers; possibly a chance of a good job offer; and so on.
But Linus Torvalds doesn't make money from increased Linux usage. Richard Stallman doesn't get money from increased GNU usage. All those servers running OpenBSD and OpenSSH don't put a penny into the OpenBSD project's pockets.
1. The Cathedral and the Bazaar: http://www.catb.org/esr/writings/cathedral-bazaar/cathedral-...
2. Linux is Not Windows: http://linux.oneandoneis2.org/LNW.htm