Will index keywords improve search functionality if...

[spatte22]

... the index is not enabled in the skin?

My understanding is that adding an index to an html output will significantly increase build times. Additionally, my team's project won't actually rely/use an index, we just want to improve our search accuracy.

My research so far leads me to think that yes, simply adding index keywords would help, even if I did not have a physical index available for users to see/use.

[NorthEast]

My understanding is that adding an index to an html output will significantly increase build times.

I disagree with that. I'd be surprised if there's a noticeable increase.

My research so far leads me to think that yes, simply adding index keywords would help, even if I did not have a physical index available for users to see/use.

Yes, you've answered your own question. Index keywords are included in the search by default (you can Exclude index entries in the target).
Including the index tab in the skin has no effect on the search - and some skins don't have an index tab (top nav and side nav).

[spatte22]

Thanks, Dave

My understanding is that adding an index to an html output will significantly increase build times.

I disagree with that. I'd be surprised if there's a noticeable increase.

oh really!? I'll have to test it out to see what(or if) the effect is. We have a pretty huge project, so we'll see if that is a factor.