They mentioned carpet “issues”, which I’m assuming is the high traffic areas. 

Due to water damage, we scheduled contractors to come out and fix the carpet and whatnot.

I typically do only minor updates (fresh paint, new fixtures/carpet if needed, & outlets (to freshen the place up)) however on my last one I did a much more extensive update (flooring, doors, bathroom & kitchen) while expensive, I think I’ll make it back over the next 5 years because I was able to increase rent on the unit by over 50%....I’m sure there are folks with more experience than me, but just wanted to share how I approached the decision.

-I replaced carpet in the basement and had some drywall work done where some had to be removed.

I've seen these things eat chunks of grease-soaked drywall and wood from cabinets, so if  you've got some saturated wood in the cabinet, cleaning the surface won't get rid of them.You might also have to change carpets also - since there's really no way to fully clean carpet...I've also seen german roaches infesting a burned out unit feasting on burned greasy cabinets and walls.   

I managed a 120 unit complex, all turns were done in 24 hours,Painting, carpet cleaning, turn cleaning, locks, we had a well managed crew and averaged 5 to 12 (during usually June) turns a month.  

Or they say "the place just needs touch up paint"  or "the carpet just needs cleaning" when in fact the whole place needs painting or the carpet needs to be replaced.

IMO with pets, it depends on the floors, do you have carpet? 

(the 4plex) I know some paint, carpets and appliances could drive up rent. 

They left the whole house and the carpet very dirty.