I suspect these are portfolio loans. 

Ummm... that's really probably rather tricky, legally... the problem is, once a human being dies, his entire existence is folded into an entity called "his estate"... that includes all his debts and responsibilities... so, for example, I would suspect that the only entity which could legally deal with a change in the value of the "estate" (i.e., any addition or reduction of value) would be the "executor" of the "estate", whoever that might be.

Currently I have a cheaper 3-piece tub surround in each unit but I'm having issues with the caulk peeling off and it's very suspect to mildew and growing some mold.

What I have that is 2 story hasn't had any trouble renting, but the neighborhood is good, the house is nice, etc and I suspect that's a bigger factor. 

If they already suspect $30,000 in foundation repair, they don't want to KNOW that it is there.

I highly suspect you can find many RE based investments that would project better return than these options at these construction costs.  

Every insurance policy is different, but I suspect they will not pay for it.

I suspect this is a result to me raising the rent 10%, but I'm not sure.

I would double check I suspect HOA liens get removed as well since they are junior to the tax .. over the years we bought literally hundreds if not more than a thousand parcels in CA at tax sale and never once had a lien survive.. the only bummer was we got one over turned when the county missed the statutory publishing date  ( 21 days) by one day and the owner who lost the property brought a civil suit and the judge reversed it.. the entire sale that year could have been reversed over 250 properties but each and every own would have had to bring a civil suit.. then after one year there is NO ability to reverse the sale. and of course we got our money back.. but spent money on attorney. 

I suspect this reflects the national trend that sees quality of life in many cities degrading which is causing an exodus to the burbs and rural areas.