If you can't get straight over the top of Snowdonia then I suggest routing to WPL then due West to Aberdovey estuary.
The hills you have to flyover are below 2000ft and are all rather flat topped and boggy - much nicer to glide/crash on than their rather steeper rockier North Wales cousins.
The VFR nav is easy as there is a sodding great railway line to pick up thst will guide you in South of Machynlleth. There are also some useful windfarms enroute. It takes only 30 mins from overhead WPL to Aberdovey.
Once you are in the estuary its easy to turn right and follow the coast to Anglesey.
Compared to routing up towards Wreham, LPL and then across the North coast this route:
a) requires a lot less r/t work
b) requires lower msa's
c) flies over better forced landing terrain
d) minimises any inadvertant straying into controlled airspace
e) has less traffic to see and avoid
f) is easier for VFR nav but radio nav is near impossible
g) going there this way then back the other way along the North Wales coast route will mean you don't have to cover the same scenery twice.
Good luck, its a nice trip.
WWW