Allowing touch spells to be made persistent is pretty huge if you did not allow it before with other metamagic additions (which I personally dont think works normally). That is alot more spells you can use persist, which in turn will result in the second biggest effect on the game, the amount of time you are now going to spend finding those spells.
While the modification to the adjustment based on spell duration is interesting, I dont think it will have must impact on the game. Most spells with an hour/level duration are extended early and cast normally late in the game. Spells that last rounds per level were made persistent with real spell slots late in the game (level 1-3 spells), but that wont be possible now with the adjustment of +8. Really though, how many characters actually cast persistent spells without some huge metamagic reducer? Even the minute per level spells only get their legitimate range increased from 1-3rd level to 1-4th. I still think the driving power to persist spells will still come from Divine metamagic and other reducing tricks.
This sort of reminds me of a third party feat from the Book of ultimate feats (orginal source Legend and Lairs). It is called Lasting Spell with a level adjustment of +3 and a feat pre-req of extend spell. What it did was increase the duration by one step.
Round/ Minute/10 Minutes/ Hour/ Day/ Week/ Month/ Season/ Year/ Decade/ Century
For each additional +1 adjustment it would increase it one additional step, but the extra steps also required an additional spell slot. For instance:
Divine Power L4 normally Rounds/level
+3 Base to make it minutes/ level would be a 7th level slot
+1 Additional makes it 10 minutes/level for a 7th and 8th level slot
+1 Additional makes it 1 hour/level for a 7th, 8th, and 9th level slot
In some ways I think this feat is a little more balanced than persistent spell as it currently stands. You could boost any spells duration, but it took alot more slots if you were pushing it up several categories. Now of course you get into trouble like persistent with metamagic reduces, more so when you get your spells to last weeks per level at a time. And of course with the standard Cheater of Mystra build, that results in a hell of alot of supernatural abilities that never go away.