Yes, it is usually cheaper to make what you already have better and more functional. If you can make a few modifications and make the area suit your needs, you will be money ahead. Can you move the walk thru door and make it normal?
Having all your wood working tools on casters sure makes it easier to move things out of the way for vehicles. You must not have many thieves around there...
The walk through door could be moved but its in the same wall where the drive through garage door would be installed so it would certainly be getting moved.
There's a 48" walk through door on the south side of the shop already, the west side was setup for horse stalls so there are 2 doors on that end but they are split so you could open just the upper half and leave the bottom section closed, both of those doors need to be completely removed as they are not installed properly and there are terrible gaps in them making any sort of heating or cooling of the building impossible.
The plan so far is to add the lean to onto the west side since those doors are in need of removal, get that area all done and floor put in, get all the tools moved over there out of the way, then concentrate on the rest of the shop as I have the time and extra money, probably in the spring I'll get all this stuff started, winter is creeping up on us now so I may do some of the interior work that I've been wanting to get done, like finishing the inside with insulation, and putting some sort of wall board up, thinking about sheathing, it can be painted, and would be great as you can put a nail or screw anywhere in the wall to hang stuff rather than finding a stud through drywall.
The shop right now I can't remember for sure but seems like its a 24' x 36', so its not that bad for size as it is, its just not very well designed on the ends. Course it is actually a barn and was used for horses and hay storage for many years, so at that time it served its purpose, but now its just not setup for what I need. I need a barn remodel LOL.