I can't advise on the Dynaudio as I didn't spec it having been unimpressed with the set up in my mk6 (which might have just been down to me not setting it up properly) BUT mk7 owners report a vast improvement so if you're keeping the car long term you'd best tick that box as regret is not something you want. The £500 or whatever will easily be swallowed up in five to ten years if that is indeed how long you keep the car.
I went light on the options as I have a terrible habit of changing every 18 months to 2 years and looking at my mk6 history taught me a lesson I won't forget in a hurry.
Both my mk6's were bought used but only a few months old. The first I specced really lightly and lost very little money. The second would have cost £32k new due to all the extras and brought in £16k at two and a half years old!!! OUCH! Glad I bought it at a really big saving but I still lost a lot of money.
So I was a bit wary with the mk7. Just the cheapo options ticked aside from the basic nav which is still expensive for what it offers above the standard radio system. I ticked that box for the convenience of the nav (which I hardly use) and the fact that in a couple of years it will be something a buyer will look for so
might add a little to the value but will certainly make it easier to sell. However, if in your position of keeping the car long term I'd not bother, you sum it up pretty well.
As above there, keyless is probably something that will be standard in a few years so maybe worth speccing. I didn't bother as it doesn't appeal to me, my dad has it in his crappy Nissan and it's not without inconveniences in itself at times.
DCC might be useful but again, long term there's lots to go wrong!
And to the all important £££££ bit.
Lots of the best deals on here are from brokers that will mean you have to sell your car privately. So if you have time and patience and a bit of luck it's win win for you there. Better return on your old car and an easy 10% plus.
If you're using a local dealer then the convenience is worth a few quid, but more importantly if they're giving you top book price on your car then I think there's only so much room they have in the deal (buying from retail dept not fleet with no p/x as brokers tend to deal with).
https://www.capconnect.co.uk/ConsumerValues/Ford.aspx?DB=CAR&CH=PWRTZ&New=1 is a good site to check the trade value of your part ex.
This is the guide your dealer will use in a slightly more advanced form and CAP who run that price guide do the forecasts your dealer will use for potential depreciation on the part ex hence their estimate of £200 a month or so (which gets less as the car gets older and is just a GUIDE).
If you're not 100% on the deal your dealer gives you it only takes an hour or so of ringing around a few dealers people mention on here with the bigger discounts to see what they can do for you.
Some of it timing, some luck and some through being a persistent negotiator!!!
If you're planning a long term relationship with the car and dealer that's worth a bit of money to you and to them so just see and push for the best you can get without souring either them or you.