In my opinion the answer is yes
Heat rises by convection, but this is not the only way it travels.
In my victorian house I have exposed floor boards sat on joists, literally over the ground. I have lifted all these, insulated between the joists and relayed them. The difference is unbelieveable, though admittedly they are not T&G, just butted. You need to keep the underside well vented to prevent condensation/moisture.
It is however a matter of personal opinion and choice, others will not notice the cold coming up from the floor but I do. Just depends how much you want to over engineer your workshop. I wouls say go for it, the cost will be minimal extra and very difficult to do as a retro fit.
Mark