Is this excessive wear? Re-buildable? (Empyre 100)

Not quite sure - are you talking about & showing refractory wear with the pics, or is there some corrosion going on in pic 1? Are there leaks? A pressure test would definitely be in order before even thinking about it. The brick stuff in pic 2 looks like an easy one - although I'm not familiar with the construction of it. I would also find out if return temperature protection was in place while the boiler was being used.

You might find some interesting reading here if you search this boiler, if you haven't yet. I think there were updates or design changes made to it along the way so might want to check those out & see if they are a factor here or should be done. Can you get a peek inside the water jacket with a flashlight thru a port?

Replacement refractory components should cost around $200-300 at most. If the steel is in decent shape you're looking at a good deal for that price imo.

There's been some problems with them, but if you can get it cheap enough...

If you do a search here and spend some time reading about Empyre you will have your answer. From what I have read I would RUN

gg

My 200 is working good and saving me a huge amount compared to burning oil. the bricks are not hard to replace, they replaced a few of mine at no charge. Sounds like you are going to get it for a couple thousand dollars, If it holds water I would be all over it. When it craps out get something that will replace it. It looks like you could get a season out of the bricks as is.