Is there no hidden service menu on early Vestels like my Digihome DTR 160?

I haven't even found the option to display muxes, freqs and signal strengths. Esssential for reception fault finding.

Do the latest HD Vestels offers this stuff, as the pricing is quite tempting?

There is a test menu which can be accessed after a factory reset - it can be accessed using a serial terminal program via the RS232 port, but I don't remember if there is some magic button press on the remote for it. That said, I shouldn't really bother mentioning it as it contains nothing interesting - just has a few items for testing if the box is faulty, etc.

Anyway, what you need is the manual channel scan screen. This can be accessed via the regular menus on any Vestel PVR, and will display the signal strength of the mux of the currently tuned channel (UHF channel can be keyed in if you know the muxes). The latest HD models are exactly the same in this respect.