Not necessarily too much of a diversion,but a stop at Ludlow is an idea?It is one of,if perhaps our finest town/market towns.From Ludlow,quick stops/drive throughs at Church Stretton and Bishops castle before continuing to Conwy...this may add 90 minutes driving time to your journey plus your stops.
Have a look at this route.
You would have to check timings.
Worcester to Rhayader is great countryside driving and from Rhayader you head into the mountains.
Cutting off west there will take you through nice country and you can have a look at various things before you get to Bala - a detour round Lake Vrynwy on very steep windy roads, or there is a famous waterfall called Pistyll Rhaeadr and an ancient church at Pennant Mellangel. If you wanted a longer stop then Powis Castle just to the south or Chirk to the north would take up a few hours, but by now you will know how much time you actually have. If you have not detoured, you come down through Bala on the B4391 and pick this number up again to Ffestiniog, and then on to Conwy in an hour Some very scenic, quiet roads for you.
The first part is a slog, but then it is over.