Another place BLOCK! might go well could be using numbered substitutions, which seems like convenient default:
>> reword "Foo $1 Bar $2" [1000 + 20, 300 + 4]
== "Foo 1020 Bar 304"
But... dialects are powerful.
I dunno. I kind of like the "you get what you pay for" idea... if your specification is nuanced and mean, you should have the burden of more decorations or refinements... you're the weirdo 
So this seems like the best use of BLOCK! as the reword spec.