When I bought my boat last year it came with an old Calkins galvanized trailer. I was thinking of upgrading to an aluminum trailer because it is light and everything would be new, but I didn't. Here is a few of my reasons, and just my reasons, they could be bad reasons but at the time seemed logical...
1) Didn't know what to do with the old trailer, it wasn't worth anything.
2) Even though the galvanized trailer is heavy the boat is balanced correctly, so moving the boat around by hand isn't hard. I was also afraid having a light boat and a light trailer might cause it to bounce or not track well.
3) I was restoring my DS1 so why not restore the trailer? I have time on my hands (not really that much time)
4) It can't be hard to replace every piece of hardware on the trailer. (yeah it is tracking down ubolts, ect.
5) I wanted to upgrade to LED lights, after all this is a marine trailer.
6) I didn't want to spend more then I paid for the boat and the trailer on a new trailer. (I spent $250 on the boat, and to date haven't spent more then $120 bringing the trailer back to life).
There you have my thoughts/opinions.
Marc