What makes you think OmniGraffle is near to a major (paid) upgrade? The version number asymptotically approaching 2.0? Fear not, OmniFocus for iPhone is at 1.15—the numbers on the right of the decimal point are independent of the numbers to the left, and are not a decimal fraction as the format suggests. Previous revisions included 1.14.2 and 1.14.1.
Also, and perhaps even more compelling, Omni has yet to release a paid upgrade for any of its iOS apps, one of which (OmniFocus for iPhone) has been in the field much longer than OmniGraffle, with continuing development all along. That's not to say they won't ever do a paid upgrade, but Omni's history has shown that they come infrequently and include substantial change. We just got a reworking of the drawing tools in OmniGraffle as a free update, which seems like an unlikely thing to ship if you've got a major release coming up. They'll need an impressive list of features to justify repurchasing the app (or some headache with in-app purchases), so coupling that with most of their effort being focused elsewhere, I'll predict that this time next year, the OmniGraffle for iPad version number will still be 1.<something>. If you have a need for the tool, $1/week should be easily swallowed, and who's to say that even if the next major release comes out a year from now that it will offer compelling value for you to upgrade? The current version won't suddenly stop working.