Personally, I use http://furius.ca/beancount/ as I find it much more hackable (python) and stricter, additionally it's got an amazing webui https://github.com/beancount/fava
This looks nice, might give it a try later today.
I have been using this setup for the past one year. I have added a lot of things that I use almost regularly.
The Reports look really comprehensive and crisp. I will definitely use it. Thanks!
For me primarily: If you do envelope type budgeting, GnuCash does not support it. ledger/hledger does with virtual transactions (although hledger discourages it).
Other than that, I think there are other benefits. I could never remember the ledger/hledger syntax, but they conveniently let you export to csv, and I use Python scripts with pandas to extract what I want.
If there's any calculation you would like to do, it's easier with these tools. Say, for example, you want to calculate the effective rate of return for all your investments combined. I don't think GnuCash will let you do that across accounts, etc.
You original journal file that you were using with ledger should just work with hlegder.