So when my friend first introduced me to this game he showed me some of his finished tanks and I was amazed at the detail but didn't like that they were so incredibly light...especially since you are using them in a game as game pieces. I decided that as I built mine I would add a little bit of weight inside the hull of each tank so they felt more like matchbox cars and were less prone to moving when bumping them on the gaming table. I've used small nuts, bolts, or even fishing weights hot glued anywhere they will fit in the hull without blocking the "peg hole" at the top.

Has anyone else done this, or is it just me?

No weights for me. The big attraction is that I can load up my carry bags and not worry about dropping one and smashing barrels etc., not to mention the ease of carrying.
I just wish FOW did this years ago so I wouldn't have a ton (slight exaggeration) of resin/lead.

Weighted tanks have no appeal to me. I kind of like the low weight of the models. I'm not even magnetizing turrets. I do know a guy who, due to space restrictions, printed out a 3'x3' playmat on paper, mounted it to a magnetic board on his wall, then put magnets in the treads of his tanks and now plays on a vertical surface.

And while I do not add weights to my tanks, I do glue heavy washers to the bottoms of my x-wing bases. I want to minimize the occurrences of me knocking over those spacecraft.

I have a mix of some FOW resin/lead models and the BattleFront/GF9 plastic Tanks. Sometimes I'm a little hard on the plastic minis when I mistake them for the heavier ones during a game. Perhaps if I started adding weights I could minimize that.