I'd go for a 1/72nd scale or 15mm (roughly 1/100th scale) version, mainly for infantry scenarios and RP action.
I've already got about 4 or 5 of the old plastic Robowhatchamacallits in 1/72nd scale, so they'd fit right in. Never could seem to get my greedy paws on a Glaug officer pod (Marauder), though. Come to think of it, I suspect that a lot of "non-players" would buy a 1/72nd plastic model kit of a decent looking Battlemech.
In that size range, there's no shortage of stuff "in scale". Even HO (1/87th scale) model RR buildings would be in the general ballpark. You're not paying an arm, leg, and left [insert name of other unmentionable body part] for each mini, either.
The infantry rules need a little work, however. Battletroops (25mm, around 1/64th scale) was good in concept, a bit awkward in practice. Never liked the variable starting spot on the damage track, either. Weapons should have the capability of burning through 6 HP with a single lucky roll, but when it happens about 75% of the time for most weapons (one shot insta-kills), it's a little extreme.
[added] Going the other way, the main advantage I can see of making smaller 'Mechs would be to play Battleforce. They'd be cheaper, but there'd also be a lot less detail. With that size, the individual unit starts becoming "insignificant", and there's already a perception issue versus another game that keeps putting bigger and bigger "toys" on the table for more mass-market appeal. I don't care for the size creep in the current game, though. It's getting harder and harder to put things in adjacent hexes, and if you've got vehicles and footsloggers in the same hex, it's a nightmare.
