You may find it worthwhile to generate the 'glow' effect programmatically using a simple gaussian blur filter. Depending on the codebase you're using, there may already be a suitable function (i.e. one for generating 'shadows')
I'd agree with the latter, though I'm not so sure about the former, mostly because I expect that most digital artists worth their salt will use similar methods anyway.
Also on the other side of the coin:
1) you can easily, dynamically change the colour of the glow on the fly 2) You can generate 'pulse' effects by changing the radius of the glow 3) You'd need a really slow computer, or truly massive amounts of large sprites, to take a noticeable CPU hit.
...unless of course you're using Flash or your target market is low-end Android phones and tablets, in which case it may not be worth the CPU hit, although I've seen some games that seem to be able to handle surprising amounts of it. GeoDefence springs to mind.
Now that we've gotten that bit of disappointment out of the way (sorry) I am a game sound designer/composer, having worked on games that placed at recent Columbia College game jams, and that were chosen for placement in Columbia College's art of play.
Not trying to sound like a braggart, just establishing that I know what I'm doing.
Sorry, but i´m a musician and sounddesigner myself (see at my website)! And I allready have some guys to compose the soundtrack with me... so, I can´t give you any commission! Anyway, thanks for your reply...