1) Absentee landlords are terrible. I can't say I know what the solution is, but perhaps simply lowering the price of the houses until the (low income) workers could afford to buy and therefore take stake in the community is preferable?
2) Unfortunately the sprawling layout of Hemet in particular is unconducive for creating the kinds of businesses that could at least mark the beginning of a more dense mixed use area. In this case there will have to be pain to raze some of the houses at the very least to help things go in that direction.
3) Broken window effect seems to be in full force with the absentee landlords only throwing fuel to the fire. Ideally the city would help some of these residents sue these landlords to resolve some of these issues, which would help slow the downward spiral of non-maintenance by the residents.