I'm not sure if you were just referring to figures part of your collection, but if not, perhaps look at branching outside of just figures if you haven't already done so?
For example, you could branch into the trading card game, or you could build the metal models (eg:
https://www.reddit.com/r/metalearth/...z_by_mu_model/ ) or ones from Metal Earth.
I know the MU line has Optimus Prime, Megatron, Soundwave, Jazz and Bumblebee (and in that reddit thread, they say starscream is coming 2019).
Metal Earth has (non-coloured / anodized) versions of the above, minus Jazz, I think.
Variety is the spice of life, so they say.
