Given most of my curry's tend to have a large amount of desiccated coconut/coconut milk powder, I might experiment with a base made with coconut oil and butter/ghee. Will let you know how I get on.

Have a look at the statistics regarding saturated fats in both options, blanchy.

I use rapeseed oil, which, I believe is healthier than butter or ghee 

Dated advice my friend.

More and more current research is now pointing towards saturated fats as being healthy, and polyunsaturated fats (the type found in refined oils) as unhealthy. If in doubt, just remember which one is a real food and which one is chemically extracted in a lab.

Most of the curry base recipes I see use a hefty amount of oil, typically vegetable oil.

Am I likely to have much success if I substitute these for either Butter or Butter Ghee?

I spotted this yesterday for the first time - waitrose have released a curry base and a range of pastes to go with it. The onion base looks pretty simple tho, just onion/garlic/ginger/chilli, and you just fry that along with one of the pastes and add meat/chopped tomoatoes etc. Anyone tried out out?

Made this earlier this evening. Followed the recipe exactly apart from using an improvised spice mix as I only had turmeric, paprika, cumin and coriander. Smells very nice, certainly much nicer than the KD base which I've been using up until this point. Hoping to use it in the next few days so will report back on the results.