Tier-2 is all you need for most alts. That gives you the full Mk X or XI sets, and the consoles. Some toons need to go higher to get access to more stuff (rep torpedoes and such), but most of them dont.
I dont have any alts. I have 5 chars with specific design objectives, and of those I am taking some of them to T5 in each rep. I want full access to the Omega sets, but theres nothing I need from T5 romulan or nukera rep on all of them.