Where to spend 'excess' points?

If you like tech, I would suggest Invasion too.  It greatly increases damage taken by enemies if spec'd correctly and this is invaluable on certain LARGER enemies......with power profiles, you can easily have your main use profile then more tailored to special situations, such as wanting to slow characters down, or remenant specific...so things such as shield drain, ice, and invasion are all good choices to be put on the 2-4 profiles.

For every point you put into a combat skill you get more HP and weapons damage.

For every point you put in biotics you get more barrier/shields and IIRC faster cooldowns(maybe area and damage too).

Fore every point you put in Tech, you get shields and tech power damage(maybe cooldowns too)

So honestly, adding in stuff you aren't going to use isn't a bad thing, and can help you in the end.  I would max tech damage skills you like, then combat(which sounds like you have done) and then just max them as you go, maybe blending skills in each to max both tech and combat...if you play enough then max biotics too just for extra shields.

Yeah this issue exists because the assumption is that you switch profiles and so you need to have enough points to use in all 3 areas (combat, tech, biotic) so that you can swap between profiles.

Personally I never use this because my trusty sniper rifle does all the work it needs to but I actually like some biotic powers, particularly shockwave as a detonator because it's a nice aoe effect that pushes all enemies away that are getting too close to me.

I really don't care for this profile swapping so I accept I might get some points but actually having a tech primer and biotic detonator works for me.

If your chosen skills are already maxxed out, look into getting your profiles to the next rank. In case for Soldier/Infiltrator that'll be more combat and tech skills, even if you won't be using them actively.