..do you know if there is a specific thread dedicated to these 'little no-namers" ?
There is a website dedicated to Scottish 9-hole courses. It's been highlighted on GCA before but for the life of me I can't find it now!
If you follow the coast northwards from St Andrews up to John O'Groats you'll find dozens of lessor namers - no offence to any I've included in this bracket or to any I've missed out - and here are some -
Scotscraig
Downfield (as you've mentioned)
Monifieth
Panmure
Carnoustie Burnside & Budden
Arbroath
Montrose (36)
Stonehaven
Balnagask (Nigg Bay) Aberdeen
Kings Links Aberdeen
Silverburn 18 at Royal Aberdeen
Murcar (as you've mentioned) have a further 9-holes as well
Rye Grass Fairways International (whoops, sorry, only kidding, couldn't resist!)
Newburgh
The (great) St Olaf 9-holer at Cruden Bay
Peterhead (27)
Inverallochy
Fraserburgh (27)
Rosehearty
Royal Tarlair
Duff House Royal (as you've mentioned)
Culllen
Strathlene
Buckpool
Spey Bay
Gramouth & Kingston
Moray at Lossiemouth (36)
Covesea
Hopeman
Nairn Dunbar
Nairn (as you've mentioned) have a further 9-holes as well
Castle Stuart (you've mentioned it)
Fortrose & Rosemarkie
Portmahomack
Tain
Bonar Bridge
Skibo/Carnigie (very pricey/exclusive)
Royal Dornoch - 36-holes inc 18-hole Struie course
Golspie
Brora
Helmsdale
Lybster
Wick
.......and theses are just the coastal courses
Unless they have access to a special deal and/or are determined to play the Dukes at St Andrew, Downfield, Murcar, Castle Stuart and Nairn they may get better value from a pick-n-mix combination from the above list. IMO Royal Dornoch, Royal Aberdeen and Cruden Bay as 'musts' though, even more so if you've traveled a long, long way.
Wherever they play I hope your close friend and partner have a great trip.
All the best.