I don't know offhand how the points work out, but it sounds like a decent move to me. When mech dominates so much, you'll probably find a lot of highpowered weaponry going to waste on single guardsmen. The thing to watch out for in terms of gameplay is other horde armies. Boyz usually mow over guard blobs without much effort. They have the same number of dudes with twice as many attacks. I'd suggest kitting out a PCS or a SWS with flamers to cover the anti-swarm angle if you have points. Usually that's covered with Hull Heavy Flamers on Chimeras or with other armored options like Valks with MRP, Hellhounds, or artillery, so your list might lack a bit in that direction.