The Diesel engines used in the Yer-2 and some Pe-8 were highly unreliable, and therefore the first type was not used so much and the latter was equipped mainly with other engines because of this issue.
You can find exact OOBs of the soviet ADD (Long Range Aviation) here:
http://ilpilot.narod.ru/vvs_tsifra/gl_3/3.118.html
Concerning their contribution to the soviet victory: I think it is not very high. In the 2nd half of the war, a lot of night attacks were flown against railway targets, depots, airfields. Success was "highly mixed", especially if you take into account the high number of "2-mots". So at least it can be said that their efficiency in 1944/45 was bad.
But how was the effect of the RAF's night offensive on allied victory? I think, only secondary by attracting Nachtjägergeschwader who might have been used as Kampfflieger otherwise.
Dénes, I really enjoyed reading your books! But, do you really think that the attacks described in your books had a great impact on the overall development of that campaign?