Since we do not know the price, it is difficult to estimate worth.
Also it is not necessary to upgrade. I'm still running one system with 10.5. three systems on 10.6, and my wife has a 10.4 system still running. I only have 1 10.7 system, and that has only been since late November.
I other words, there is not need to rush out and upgrade just because Apple releases a new version.
If you decide you must have the new app related features, then consider the OS upgrade price the cost of buying those new app features.
Now from my perspective, a new OS release that has fewer changes is more likely to be stable when it is shipped, then one that has a ton of new features where very few people have used the full set before it is released (beta testing is not the same as letting millions of customers have at it).
So for me. Smaller OS updates with fewer OS chagnes (even if you and I cannot see what those changes are) is better.