I guess that this is similar to another topic (when do you commit to a faction), but I have a specific situation. I don't think I'm committed at this point, but I plan on supporting the NCR. Caesar wants me to destroy what I find, the House wants me to activate the Securitrons, which I guess I also do for Yes Man (?)...but what should I do if siding with NCR? Or should I have avoided coming here at all?

I don't think it matters either way.

Might as well upgrade the securitrons in case you decide to switch to Yes Man later on.

Run in the halls, and shop lift!

(naw, just activate it, makes vegas safer, and the securitrons badass)

Depends on whom you serve....if you serve Caesar, do his bidding. If not, the upgrade keeps the other three options open for a while longer.