Bob
I've had a look at various sources which I will list, not a huge step forward but hope it will lead you in the right direction

First, I looked at the Ruabon parish transcriptions produced by Clwyd FHS. There is no mention here of Boliver/various alternative spellings until 1800.
Then we have:
Baptisms Mar 12 1800: Aurelia Boliver, d. of Franies
(stet) and Elizabeth, Bodylltyn
Feb 22 1801: Sophia Boliver, d. of Francis and Elizabeth, Bodylltyn
Aug 19 1803: Francis Boliver, s. of Francis and Elizabeth, Ruabon
Jan 12 1806: Edward Boliver, s. of Francis and Elizabeth, Bodylltyn
Aug 23 1812: Francis Boliver, s. of Francis and Elizabeth, Ruabon
obviously the first Francis died
Bodylltyn is the Rhosymedre part of Ruabon parish22 October 1800: William Powell, s. of William amd Sarah
Apart from confirming the marriage that you have already found in St Martins - Elizabeth Smith - I can find nothing more in the St Martins fiche from Shropshire FHS.
So no info on the parents in either of these parishes. The nearest I could see from a quick look on the IGI for births around the time one would expect were Elizabeth Smiths in Ellesmere and Oswestry and a Francis Bolver, b. Selattyn, 1765, son of Edward and Jane.
In the broad time frame that we are looking at, there was a lot of activity in the area: Thomas Telford was surveyor for the A5 Toll road and for the Ellesmere - Llangollen canal. There was also an expansion in coal mining and brick making in the area. So the Bolivers might have come in for any of these reasons or something else.
It might be worth trying to find them in the 18th century and locate their main origins. Then you might be able to have some idea of their migration.
Hope this is of some help
Gadget