IMHO you are just missing out on a huge number of awesome roads, your route skims just north of the Alps, I think much of it will still be very pleasant / excellent, but if you have never been to the Alps then you could just swing down a bit further south (the snowy bits on your map)
I also did not think much of the Eagles Nest, it is more like a Disney attraction (done badly) than a historical site, apart from Hitlers gold plated lift (That and the tunnel leading to it are only unspoilt bits) the place has been destroyed, Hitlers office is now a canteen serving glorified school dinners (at vast cost) and the large patio area you see in all the archive footage is like a pop-up food marker you get in London with a few tacky souvenir stalls thrown in.
You don't even get to drive through the main complex where all Hitlers Henchmen had houses, but you do get to see a model of it where you go to get your tickets (Yaaah!)
Talking of over-priced attractions the Grossglocker falls into the same category, huge tourist trap, giant multi-storey car park is not what I want to see at the top of a mountain pass, and hordes of other vehicles and buses chugging along in my way did not add to the experience either, having to pay for all this adds insult to injury....
....But at last you can look forward to parking up at the "bikers rest", I certainly did until I got there and found they let cars up there and there was no space for our bikes, so we just got going back to roads less travelled PDQ (YMMV of course)
Unfortunately, like the Stelvio, these are "must visit" places for many and you need to find out for yourself, you may love it, but there are better roads, and better views that cost nothing and have a lot less traffic around them.
As for route, you could head from Black Forest towards Ravensburg, then Imst picking up some nice passes, hop over the Motorway to the Timmelsjoch (toll pass, but much better than the Gross-pricing-structure-Glockner) then maybe a quick skim across the Northern end of the Dolomites before heading back towards the Grossglocker / Eagles nest.
We did a similar trip in 2013 and went across the Alps via the Vosges on the way in, onto Andermatt Andermatt (Via some great Swiss Passes)
From Andermatt to Bormio for a night (but Livigno also very good) You can easily spend a few days here (and we have in the past) but on this occasion the target was Dolomites and Austria so we pressed on.
Over the Stelvio and onto the Dolomites for a few nights (you can easily spend a week here, but we had 3 glorious days on what I consider some of the Alps finest roads)
From Dolomites to Austria for a few nights to ride the Nockalm and Grossglockner, from there we headed back past Eagles Nest and home via the Austrian Tirrol, Black Forest and Verdun.
This was 14 days door-to-door with only the first and last day not being on predominantly good - amazing roads.
Write up here:
https://www.zx14r.co.uk/phpBB3/viewtopic.php?t=9758&start=15
Pictures all missing courtesy of Photobucket