I agree this is a rare use, and in model prose the form would be nihil maius, but I do not agree that nil maioris is ungrammatical. It is probably non-classical; I found but one cite for nihil maioris--from Livy XXVII.17--and it includes rei, but some Medieval writing that I don't know enough about to vouch for (anybody heard of 16th century author Jacobus Pontanus?) does use it without rei.curiosus dixit:I respectfully disagree. The partitive genitive is very rarely used with adjectives of the third declension. "nihil maioris" sounds as odd as "nihil laudabilis" instead of "nihil laudabile". Don't take my word for it:
http://www.hhhh.org/perseant/libellus/aides/allgre/allgre.346.html
A latin scholar would without any doubt say "nihil maius" never "nihil maioris". I suggested "rei maioris" in a feeble attempt to save the rhyme the original poster seemed to like.
To avoid the problem, I'd suggest nil dolorum, nil bonorum/lucrorum. I don't necessarily like the plurals; lucrorum as general profits is barely attested in the Distichs of Cato (and here there is a variant reading lucrosum), and bonorum is somewhat abstract for the usage here.
Still other rhyming possibilities which would not incure the wrath of grammarians are as follows: nil dolitum, nil meritum and nil sublatum, nil oblatum