Go skirmish level, or start a
RPG campaign, using the figures in the game.
other Ideas are to start a ladder/ map based/ or planetary campaign at the local shop.
Use what you have, until you win units you don't....
Start with a squad, pins in a map, and fight over objectives. Sometimes you get something cool, sometimes you get additional issues that come up.
One time, I was playing one where my platoon earned an inquisitor, and ion the next game, I earned a Plague Marine.... Obviously the two didn't get along.
These days, I am starting a new
40K army with a demagogue, and a squad of cultists. Platoon level, then grow from their, along with a main character that I am writing up a Black Crusade character for.
I know exactly what your going through. It happens to me every time a new edition co0mes out and all of the asshats down at the shop jump on the lickie and chewie bandwagon, and the game becomes static.
A bonus out of this is that you can sell the smaller army if you get tired of it, and there are always customers who do not mind starting with a low army count. ( that silly thing about the overreaching prices.)
On most armies, I am solid for at least three squads, then I reach burn out and have to get some characters, or a vehicle.