(Note - the property values I'm about to mention are in the close-in DC suburbs, one of the most expensive places in the country. We do OK but I'm not a rich guy)
In 2000 bought a hideous but unmolested little - like under 1k sq/ft - 1948 brick colonial for $250k in the 20816 zip code. Attached 11 x 23 garage, tiny basement, in need of thorough renovation. Come 2010 it's about finished, and is really nice, but awfully small. I work in engineering related fields where I make prototypes and I have a ~tiny~ machine shop. Mrs. motomoron finds a much larger 1950 rambler w/ a 16 x 20 machine shop space below a large master bedroom/bath expansion and a 24 x 32 detached garage in the back yard. The asking price is around $650k. We talk to the selling agent and our agent and call the bank who tell us we can swing it.
Long story short, we buy it for $618k, and sell out place for about $615K the week it goes on the market. A month later, the buyer, having strung us along with tiny requests and negotiating contingencies, voids the contract mere hours before forfeiting their $100k earnest money.
So I continued to renovate house #2 like slave, hoping to get as much finished as possible before moving in, and we waited until February to go back on the market. Once we did, house #1 sold in a week for $625k and late March we moved into #2 with money in the bank, much more space and a mortgage that was a much smaller percentage of our annual incomes than when we'd bought #1.
So, how does this relate to shop ROI?
The new place had space for my machine shop to grow and the garage could have all the fab shop gear I'd ever wanted. A job opportunity as a contractor to a government institute came up and my ability to do comprehensive prototype machining and fabrication was a key factor to my success. I acquired the assets of a small machine shop that was being liquidated. Once combining it and what I already had and selling the excess, I was well equipped. Since then I managed to obtain another small shop that was surplus to it's owners and fully depreciated.
If I look at the cost of the move and the amount our mortgage increased vs. my income tied to having the shop, we're way ahead. Having a dedicated race shop 40' from my machine shop is a huge quality of life thing for me. So, if having the shop can potentially improve your earning potential - or just make life better in a tangible sense, I'd do it, and go big.