And as noted, you are likely dealing with plaster and lathe.From a cosmetic approach, as noted, keep things in style with the house.  

I love his style of thinking, and it reminds me of what you are talking about.

The decor and styling look like they could run in a magazine... and well... my place looks nice, but I'd have to spend $10,000 on top of what I've put into it already for my place to look like theirs.

@Shalom Benton You could do a renovation style loan, but they're usually for owner-occupants only.

I don't want to be a hard ballplayer, not my style, but don't want to just let it go either. 

Or you have to add or replace a few pieces here or there.Vents - those should also all be replaced (most roof hardware is replaced, other than the gas exhaust pipes)  Which vent TYPE would be best depends on the style and cut up of the roof.

This will allow you to use your HELOC again and again for BRRR style properties

(Age, builders, style, HVAC systems, etc.)In vegas we have two giant air returns in our hallways and air registers in every room. 

This seems most effective in theory, but may be difficult, because it hinges on whether I can realistically find like-properties where the only major difference is whether its interior style is modern vs. obsolete. 

The rest of the loan you'll get will be investment style and will require you to put 10-25% down.Based on that, I'd only put down the minimum, 0-5% and save the rest to enable you to continue investing in more properties or being able to rehab out of pocket.