Nice question.
For a dream shop, I would want something on grade, instead of B1
Big is nice, but too big (yes there would be such a thing) then you would need a bicycle to get around
If money was not object (the real definition of a dream shop) I'd move back to Canada, and buy some land just outside of my hometown, say 200 acres. I'd build a nice house for my wife and kids, all one floor, no stairs to fall down when I get old. I'd build a HUGE garage to house all of my two and four wheeled toys, and work on them too. For a wood working shop, I'd build a nice big building, I think a rectangle is better than a square, something like 60' x 120'. There would be a division of space, certainly at least a machine tool room (read NOISY) and a hand tool area, plus an office area, with computers, Big screen TV DVD etc, and a desk and draughting table etc, reference library too, as well as a nice big soft sofa for the power naps I like to take. A full bathroom with a shower, and a small kitchen space too.
The finishing room would be a separate building, it would be not far away, connected to the main shop by a closed in walkway, with a concrete floor (easier to roll the carts the work it on) the finishing room would be a full on pro type, with the stainless steel walls, the full filtration and the water under the floors thing too. Big, big enough to also paint a car or truck in.
Next to the main wood shop would be a welding shop, full on welding stuff, Tig, MIG and sticks, plus hot wrenches too. Not to mention big steel cutting band saws. Next to the welding room, in the same building would be a machine shop, lathes, mills, CNC machines.
Behind the main wood shop would be a large bandsaw mill in it's own building, so I could mill trees in any weather, and beside that would be a VERY large barn like structure with tall ceilings and good ventilation that would be my storage area for wood, and in there somewhere I'd put a commercial kiln.
I'd have power from the city etc, but I'd also have a generator or three (five?) that could run everything if needed. I've have my very own underground gasoline tank for my various two and four wheeled toys too.
I'd need a second garage for work toys, stuff like front end loaders, tractors, snow plows, fork lifts etc.
While everything was being built, I'd take a year or two and go to the US and enroll in some really good school so I could learn the basics of making fine furniture from the best teachers.
Once I was up and running, I'd start a business building fine furniture, and I'd try to hire the best and the brightest up and coming wood workers to come work for me, so I could have the chance to learn from them for a while. I'd pay them well, and treat them the best I could, giving them the freedom to do what their talent pushes them to do.............
I'd have guest house for cabins on the compound, and I'd build a large workspace with some of the basic tools needed to teach, I'd get someone in to teach classes to kids and to others that are interested in woodworking. I'd try to have seminars too, get some of the best and the most talented wood workers to come and teach and hold classes in the summer.
For fun, I'd put in a full on dirt bike area, MX and enduro, and I'd build a smaller scale race track for shifter carts and supermotard bikes. The land would have to have a small lake of some sort for fishing in as well.
Helipad would be nice too....
Well that was sure a nice little ramble
Now back to reality....
For things that I use the most in my shop, well I'd say my whole shop is the best tool/jig I've built, but really, it is all a whole, very little work would get done without all of it working together, so it is hard to pick out one or two things.
I guess my cyclone & duct work, would have to count, and the setup for my SCMS too.
Cheers!