I make most of my trees from Wirebundles, one of the Architect supply companies over here sells them specific for that purpose.
IMHO, making a good Dio has more to do with an artistic eye than modelling skill, got tons of drawings of planned dio's that most likely will never be done.
Kinda like painting a picture at times you have take artistic licence and change things a bit to get a better end-result. Your RGM78 used a very good idea and looks good.
Not sure which Book you are talking about, the one book i mentioned here is as follows:
http://www.hlj.com/cgi-perl/hljpage.cgi?HBJYMT
He is really good and his works cover a wide variety of genres, the book is a collection of his works.
Websites about building Resin Kits, there are few good ones in english and most of them barely cover the basics.
If you can get hold of try to get Japanese modeling books like the:
1.) Max Watanabe Book,
2.) Nomo-ken,
3.) Replicant.
They have TONS of pictures and you can figure what they are doing without being able to read Japanese.
Most of those books cover material description, basic techniques, resin kits and in cases even go into scultping, mold making and casting parts and figures.
Also try to get hold of the introductionary Books by Tamiya, Gunze Sangyo & Wave for their own products.
Here is a site that has the most decent info I have found so far(too many talk about what THEY did/their experience and don't really describe the techniques used):
http://www.sharexperiences.com/picforum/displayimage.php?album=2101&pos=0
If you get stuck or got a question feel free to ask here or drop me an e-mail, I have found that doing a mecha resin kit is different from a Figure resin kit and not all techniques apply equally.