Jay is well-regarded on here and I've never seen a bad word written in the 8.5 years on here.
He responded quick when I was interested in a car he had too albeit I was buying on behalf of someone else (except she didn't like the car itself sadly!).
He gets S Class Mercs now and again as I often have a peruse of his website. They are usually not far from your budget but the cars look well-priced to me and they don't hang around that long. They are obviously cared-for examples.
I am nearly 44 so I get the whole gadgets thing - I am the same.
From what I've picked up over the years, it seems a lot of early cars are well spec'd and then as time goes on they seem to dwindle.
Take the W/C216 CL500 - a lot of 2007 ones seem to have Night Vision and I hardly see that in any of the late / last ones.
I can only assume those with a shed load of cash want the cars when they come out, they spec them up but then move on not long after.
Who knows.
If you are focused on an S Class, your life is somewhat easier. You could start researching more into those to see what you get as standard and what was option so you know what is what. A lot of adverts I've seen on AT often state "Every available option" which usually means nothing of the sort. I can usually spot half a dozen things missing. I treat the adverts I read on AT as simply marketing and rely on my own knowledge.
It might be worth thinking about what options you really want - things like the fridge, Night Vision and Ventilated Seats are a bit gimmicky / a waste of time in my opinion.
The following has a lot of information on most cars if you want to swat up:
Mercedes-Benz S-Class (2006)
If you bought a CLS 350 petrol, you aren't scared of buying fuel so don't rule out an S500 for example. The higher models have more kit as standard. I reckon in the real world, a V6 and V8 petrol are pretty close on consumption - with the 500 having quite a lot more power.