You get larger companies doing a lot of Search Engine Optimization in local markets and larger companies paying lots of money for Ads.

Suggest you take a look at their keywords to help them optimize their site.

Made sure water heaters were operating optimally and replaced those that needed it.

You should be optimizing after-tax income net of perceived risk; NOT minimizing taxes. 

Special Assessments generally spook buyers so removing this potential objection is always a higher priority than trying to optimize for purchase price / payment.

I have seen that even with optimized VR websites the OTAs will still rank higher, but it is good to be in the ballgame with them there. 

I would focus on buying a handful of high quality B properties (for the optimal combination of cash flow and capital preservation/ possible appreciation) with low turnover and low maintenance costs rather than many lower-tier properties that will likely bring more issues, especially if you have to deal with Section 8 housing authority bureaucracy. 

If it drops it to a number below the ROI you could get elsewhere... why not sell it and take the profit + reinvest in optimal returns?

If so, what areas are optimal for a good cash flowing rental (minumum vacancy rates)?

You can find calculators for this using YOUR income / expenses by searching "Equity Optimization" or "Equity Advantage" input YOUR numbers and get a result.