Dear Mattias,
I found out from the Runet, that Rikhter’s heirs sold out the house long ago, and Prokofiev’s heirs are going to sell the house soon, and thereby I’m afraid that both houses could possibly be out of bounds for tourists. The new owners of houses are not planning to open museums, but use both houses for their own purposes. There is only one museum in Nikolina Gora (Officially – RANIS) – it is Veresaev’s museum opened in his house:
http://www.bes-chagda.ru/monastyr/veresaev.htm
Also I found the official site of the settlement with its history and some photos:
http://www.nicolina-gora.ru/society/cottages
Both websites are in Russian, but you can try and use Google Translate Tool (a bit crappy but better than nothing):
http://translate.google.com.
And as far as I could find, one can get to Nikolina Gora by No.150 minibus (marshrutka) from Molodezhnaya metro station. The stop you need called “Poselok Sosny” (but you know there is always a good chance to stick in a traffic jam there). It’s only in 10 minutes on foot from that stop, but I couldn’t find the direction. So try and ask somebody there.
That this is all I could find for you. Good luck with getting there. And come to hike one day!