They were very similar. I even reused the code. One was writing rules to validate giant forms, the other was writing rules to for decisions based on form responses.
Ok, just ranting on DSLs. Good DSLs take someone from can't to can. A DSL that's meant to save time is way less likely to be useful because it's very likely to not save you time.
In both of my DSLs, it's that we needed to get complex domain behavior into the program. So you either need to teach a programmer the domain, partner a programmer with a domain expert, or teach a domain expert how to program.
Putting the power in the hands of the domain expert is attractive when there's a lot of work to be done. It frees up programmers to do other things and tightens the feedback loop. If it's a deep domain, it's not like you want to send your programmer to school to learn how to do this. If it's shallow, you can probably have someone cheaper do it.
A DSL comes with a lot of cognitive overhead. If the other option is learning a full programming language, this becomes more reasonable.
A time saving DSL is where someone already knows how to write code, they just want to write less of it. This is generally not as good because the savings are marginal. Then when some programmer wants to change something, they have to learn/remember this whole DSL instead of more straightforward code.
Actually, this makes a simpler rule of thumb. A DSL for programmers is less likely to be a good idea than a DSL for non-programmers.