I don't think it's a good idea to sand the rim down for to improve the aesthetics unless this is a show bike you don't plan to ride. If you're planning to ride the bike, leave as much metal on the rim as you can. Taking more off will only further weaken the it. Either ride it as it is, or replace it.

I've worn out rims twice, both on folding bikes on which I was commuting. Both were relatively cheap Chinese-made aluminum rims; in both cases it was the rear wheel that went. Clearly it is not necessary to use the rear brake as much as I do, but I habitually brake with both hands, and since the rear doesn't do much I probably squeeze it harder than the front. Anyway, in both cases a crack developed and the side of the rim --the braking surface-- started to bulge.

The first time this happened, it was by the seam, and the brake developed a sharp jolt with every revolution. I let a lot of air out of the tire and rode home, some twelve miles, expecting it to fail at any time. In retrospect I think I overreacted; when I took the tire off and played with the rim, I found it was still very strong at the bead. And anyway, a rear wheel failure is not nearly as dangerous as a front one.

The second time was similar, but presented as a gentle brake rub.

Bear in mind that these were on small wheels-- the first was a 16" and the second a 20"-- so the rim got a lot more wear than a larger one.

Though I say I overreacted, I'm not sure overreacting is a bad thing in such cases.