How do I know if I'm overcapitalizing?

[Gregory Lee]

I recently purchased a duplex (living in side, renting out the other). There are some things which will most likely need to be ugraded within the next 5 years. I live in Oklahoma where the market has slowed down to nearly static, but certainly not suffered as much as the west coast, etc.
Still I don't want to over-capitalize since I bought it for only $150K. There are some things which may need to be upgraded within the next 5 years:

Siding - currently there is masonite siding which is prone to deteriorate over time; Probably needs to be pained in a few years and there are some spots which are damaged. Painting and repair would cost $4000-5000 at my estimate. Another alternative is:

Vinyl siding - this will be a lot less maintenance but cost will be at least $10,000

Both air conditioning units are 25 years old (as old as the duplex) and could go out at any time. Replacing both units would cost at least $10,000.

Another way to spend the $10,000 is on interior upgrades, eg. Kitchen and bathroom. The current condition isn't bad, just a little outdated. I could spend it as such:
$3000 x 2 granite benches
$1000x 4 bathrooms - replace vanity, vanity top, faucet, change flooring to plank vinyl.
But of course this last option is just luxury and by no means essential.

Out these three upgrades (vinyl siding, A/C and kitchen/bathroom), which would you recommend I do first, to help increase the value of the property (based on the fact that I may sell this duplex in 5, 7 or 10 years from now).

Any advice would be greatly appreciated! :D