The Pro is presently £900 on
Halfords (assuming that's the same as what you've got - spec does change over time) so being quoted £700 for frame and forks plus labour/time/effort to build it doesn't seem like an economical choice.
Personally speaking, I think unless you've got a great groupset/finishing kit and it's in great condition I would sell off what's still in good order and put the money towards a new bike.
The Boardman Hybrid Team is [probably] the exact same frame as yours (specs suggest it is) and that's currently £649 (possible to get lower than this with discounts, cashback). You could buy that model and swap over your existing [better] components to the new bike and sell what comes with the Team as new. A wild guess is that you'd be looking at getting £100-200 for the components.
Alternatively, buy a different frame/form combo elsewhere and fit the bike up. It'll not be a Boardman any longer of course.
As for future/resale value anything that changes the bike from what it was to something different will hurt values unless you've upgraded it (even then you're never likely to see anything close to what was spent).
