If I were you... I would rather think of what lenses to get than to worry about camera bodies with or without vertical grip. Anyway, it is the lenses that will very much affect the pictures.
A better choice is that, go and shop for a good lens and you'd see the difference in you pictures. For that you will definitely appreciate your D70 even more. From what I see, you have not understand the potential of the D70 enough that's why you wanna to get one with a vertical grip.
My advice is that, if you have the extra cash now, invest in a good pro lens and explore or exploit your D70 to the fullest. Then in the meantime, save and wait for a newer body, say D100 replacement which is rumoured to come with a built-in vertical grip.
For which lens to buy, do feel free to contact me 96456423 or espn. Both espn and myself would be glad to help you BUY! BUY! BUY!... ;p