That is major surgery, very expensive and will not warrant an increase in rent.

Recently (last week)  i added door sweeps, weather strips to all exterior doors and door sweeps to all interior doors which needed them, bought them plastic to install over (new) windows. and have scheduled to get the furnace cleaned professionallyThe market rate of the apartment is 875 and i  am renting it to them for 800 should i be concerned that they are upset about high electric bills,  given i have done more than a slum lord to ensure they are happy and they are 75 dollars under market rat?  

This isn't brain surgery.

For example, if you put one of those locked plastic boxes over the thermostat, they'll put a ice bag on the box if they want more heat.

The daughter then got a written warning that all trash in the containers had to be in plastic bags that are also to be tied, (& I thought plastic bags in dump sites was a issue).

Like Jeff said can replace some if you have to but is MUCH more durable and clean proof than any fiberglass or plastic surround.

Buildings almost always use the cheapest of everything...including a $2 plastic vent boot instead of the $15 aluminum based vent boots that perform way better.  

Finally, cover the crawl space soil with a plastic vapor barrier.I like the remove baseboard and bottom two feet of drywall.

So we have one of those plastic extenders that we put on the end of the white pipe.

You can get a lot of mileage out of remodeling those two spaces, but you can't change the layouts without doing serious surgery on the thickset mortar bed under the tile on that floor, you can't move walls without also finding a way to deal with the floors and that wetwall chock full of plumbing,  so you're stuck with two small bathrooms.