I like the Leatherman diamond file (Wave, PST II, Pulse) precisely for that reason. Obviously, a bigger and better sharpener should be used for any serious work; but it's reasonably sized (2.5" long) for touching up folders and evn smaller fixed blades. I've used it probably a couple dozen times and it hasn't worn significantly.
Also, I've smoothed the spine (opposite hacksaw teeth) with my Sharpmaker and use it to steel edges on my daily folder. In fact, I tend to use it as a steel more often than as a sharpener.
Lastly, should it wear down, just get it replaced. Leatherman has a good reputation for honoring its warranty.
My .02 --
Glen