IMOA the mystery of CAD is the more your involved in repairing, buying, trading and collecting information on saws, Cad digs into you like a tick.
Soon enough you won't be able to resist a mini mac until you learn the lesson that there a PITA to work on for what they are worth.
It just depends on what types of saws you want to collect. If I can see a value of a certain brand of a parts saw I'll keep it. You may think
it's a long shot to find parts for it, but before you know it you find another one, and another one, and another one. Soon you'll be well along with your
2 or 3 saw plan until your into your 25, 50, 100+. I have a friend that's way over 250+ saws in his stable. He sells some and buys some all the time.
With that said on to answering your questions.
#1 If you make a living repairing saws for others it depends on what the customer wants to spend.
If it is your hobby repairing saws for yourself or others, when it is not enjoyable or you run out of storage space that when it's not worth working on.
#2 In my collection there are no shelf Queens they all see action some more than others.
#3 When you are embarrassed to tell your friend what you have invested in it, you probably have a money pit.
#4 Sure the Brand or make of a saw weighs heavy on your decision. Example, Solo Twin, Contra Lightning, Sachs Dolmar 166
And a 100 0r more I could name. That's why it's called CAD, you can suppress it at times but for sure it's not curable.