I'm against refinishing unless it is absolutely necessary. When I am trying to figure out what that "absolutely necessary" threshold is, I consider two aspects. One has to do with how bad the finish is. A little wear or crazing does not induce me to even think about refinishing. Finish that is flaking off or about to is another story. The other consideration is value, and of course, this is related to the first concern. If an ukulele's value is diminished, let's say for the sake of argument, by 40%, but the ukulele in question is in such bad shape that it's worth less than that much as is, it's time to consider doing some work, or having some work done. Even in these instances, I am loathe to refinish. There are better alternatives. In one of the albums on my profile page I have some before and after pictures of a Hollywood Concert ukulele. It was in horrible shape when I got it: big cracks, missing bridge and inlays, cracked braces, etc. But the worst of it was the finish. About half of it was already gone. The rest was crazed badly enough that it wouldn't be long before it came off altogether. The darker areas on the upper bouts were dark because of dirt. When I cleaned it, it was bare wood, and pretty badly chewed up at that. If you look at the pictures, you will see a lot of whitish streaks running down the top. It seems somebody poured some booze on it, maybe even a few times. The instrument had clearly been abused. I sought the advice of some luthiers I respect. Rick Turner's advice was particularly helpful.
The first thing I did was use an amalgamator to re-adhere the flaking finish. Here's a link to Frank Ford's site about amalgamating a failed finish:
http://www.frets.com/FretsPages/Luthier/Technique/Finish/Lacquer/Amalgamator/amalgamator1.html
Then I sealed everything with a few thin layers of shellac. Using some wood dyes mixed with shellac, I carefully painted in the areas where the color had been lost (upper bouts) to match the surrounding areas, and built up successive layers of shellac, sanding lightly in between coats, until everything was level. After this had dried for a while, I used 0000 steel wool to eliminate scratches. Actually, I made a very fine scratch pattern going with the grain so that it is invisible. Lastly, I used the steel wool with wool lube to polish it to a desirable degree of sheen.
Ostensibly, sanding off the old finish and starting over would have been faster, but the process I used, I think anyway, is preferable for a few reasons. It still has some of that patina. I didn't fill in all of the dings. It is less sterile in appearance than refinishing. Also, the shellac is removable, although I'm not sure why anyone would want to go back to the mess it was before.
Most of this stuff I learned about through conversations on this forum. In the end, however, understanding that I learn much faster and better if I have someone who know what they are doing show me, I sought out instruction. I found an antique finish expert. I pumped a lot of time and money into the instrument and my instruction, but to me it was worth it. It might not be for others, and I'm not sure if what I have in the instrument is more than it's worth. I mean to say it was a labor of love rather than one done in consideration of investment value.