yes, go with a new brushless motor setup. it would be worth it to spend the extra money in a brushless setup, rather than to keep on replacing and maintaining brushed motors.
the only thing that is that you already have so many brushed motors. your best solution in this case, would be to purchase a brushed/brushless speed controller like a novak ss+ or lrp sphere esc. that way, you can run alll of the brushed motors that you have untill they wear out, and then use your brushless motors.
if you are worried about speed, then i would say to pick the neo one brushless motor instead of the ss5800, because the neo motor has a higher kv rating (its faster). it made a 2wd electric buggy go 40 mph in the last review that i read about it, whereas the ss5800 topped out at 35.
you should also look at the novak GTB brushless racing system.