I assume you are asking if it is better for you to #1 buy the property and evict the tenant and put in $10k in repairs to increase the rent or #2 just keep the tenant in there and put in few repairs and ride it out. 

pid=1563Houston Real Estate Highlights in August(* asterisk denotes that the “Harvey effect” has been removed): Single-family home sales rose 7.6 percent year-over-year, with 5,844 units sold*;Days on Market (DOM) for single-family homes declined slightly to 49 days;Total property sales jumped 36.8 percent, with 9,978 units sold;Total dollar volume increased 40.1 percent to $2.86 billion;The single-family home median price rose 3.0 percent to $236,870, reaching an August high;The single-family home average price also achieved an August record, rising 1.9 percent to $300,670;Single-family homes months of inventory was at a 4.1-months supply, down from 4.3 months last August and equal to the national level;Townhome/condominium sales rose 12.3 percent year-over-year, with 457 units sold in 2018 compared to 407 one year earlier*;Leases of single-family homes rose 7.6 percent with the average rent up 3.4 percent to $1,926*;Volume of townhome/condominium leases fell 8.6 percent with the average rent up 5.5 percent to $1,639*.

Currently each unit has their own electric meter and I am thinking about changing the heat system to Ductless Mini Splits for each unit so each unit will pay for the heat they use and they also will now have A/C which will allow me increase rent for that amenity. 

No amount of cleaning will restore the void of color/bleach stains and the discoloration due to urine from their dog.For the floors, we only estimated a small charge to try and sand and refinish the floors, which we have since found can not be done; the entire floor would need to be pulled out and replaced with new. 

When I renew a lease, I do get price up: the better the tenant the less increase.If your state doesn't regulate the increase, send them new lease to renew with new market price.

Houston Real Estate Highlights in August(* asterisk denotes that the “Harvey effect” has been removed): Single-family home sales rose 7.6 percent year-over-year, with 5,844 units sold*;Days on Market (DOM) for single-family homes declined slightly to 49 days;Total property sales jumped 36.8 percent, with 9,978 units sold;Total dollar volume increased 40.1 percent to $2.86 billion;The single-family home median price rose 3.0 percent to $236,870, reaching an August high;The single-family home average price also achieved an August record, rising 1.9 percent to $300,670;Single-family homes months of inventory was at a 4.1-months supply, down from 4.3 months last August and equal to the national level;Townhome/condominium sales rose 12.3 percent year-over-year, with 457 units sold in 2018 compared to 407 one year earlier*;Leases of single-family homes rose 7.6 percent with the average rent up 3.4 percent to $1,926*;Volume of townhome/condominium leases fell 8.6 percent with the average rent up 5.5 percent to $1,639*HAR https://www.har.com/content/newsroom?

We included a 60 day notice of rent increase (5%) right in the new rental agreement  for the month to month tenants. 

If it is lead paint on the inside the remediation could be huge.In some cases if density levels have increased for zoning the answer might be to tear it down and build new.

What are some little "inexpensive" add-on / upgrades can I do to the home help increase the rent while at the same time giving them the security that I am trying to make this place better for them?

You need to concentrate on improving your employment situation and increasing your income.