The small metal bars are there from the factory for a reason. The nature of the original vinyl keeps the material from completely bonding to the fiberglass material the dash is made of with just an adhesive.
Even with them, there is some degree of movement of the vinyl from expansion and contraction and that is unavoidable. It is a side effect of the design of the dash.
Time wise of the dash in and out, considering all of the connections that you need to make is about a day in and a day out. You can cosmetically damage some of the components that you need to disconnect and it is possible to crack the front windshield glass under certain conditions.
This isn't a simple undertaking at all.
Keep in mind that screwing with the original Detomaso wiring harness under the dash is not child's play. It is more of a nightmare and you want to avoid handling the thing at all unless you are VERY experienced with identifying each and everyone on sight. They are not labeled and it is very easy to get confused.
There are several "updated" versions of the factory wiring diagram and basically, they are all like "tits on a bull...totally useless".
Working on it requires a lot of concentration and documenting of what gets connected to what with something like a Ptouch label maker. This is not for the faint of heart.
Apparently the harness can vary according to the time period in which the car was built as well further complicating using the factory wiring diagrams? Some harnesses from the factory have pigtails spliced in that do not have continuous color codes.
At some point with the dash out, you will need to deal with the fuse panel and you need to keep track of the polarity of the wires, i.e., which side of the fuses they go to. The factory used different phasing of the stripes on the stripped wires to keep track of that.
I would leave the thing alone unless the loose vinyl is so severe that it looks like the car was in some sort of disaster like a flood or fire.
I've had mine out several times and even switched from a dual pod to a single pod and still find confusion on some of the big circuit carrying wires that seem to be redundant in certain cases.
In addition, those quick connect wire ends on the Bosh or Lucas switches come loose easily once connected and disconnect and will add to the short circuit fire hazards if they ground out.
All that isn't worth the risks if it is just for a low level cosmetic issue that will reoccur after you have corrected it.