OldSteve:
Well, it's pretty clear by the degree of support that I'm the only one who thinks this would be a good feature to incorporate into the IDE, so it's probably best to just forget that I posted this suggestion.
No, you're not and no, it's not... I'm having the same question since I also have the very same issue. Trust me, we're not the only ones.
To me, it would be normal and logically if the board could be saved with the .ino file of a project since having different boards laying on your table is really not an exception.
I have different Arduino's, ESP8266 and ATTiny85 boards with which I'm working and each and every time I'm hitting the same stone (must be stupidity, I guess): forgot to change the board and bang... building is OK but uploading is, of course, not...
Hope this will change in the future.
Best,
Geert