If it ain't broke, don't fix it.
Seriously.
If you find a plugged injector 100,000 miles from now, it's a HECK of a lot less work to pull it out than it was the heads.
Unless you put contaminated fuel in your tank AND it somehow gets past the filter, your injectors will easily outlast the rest of the vehicle.
If you want to set your mind at rest, drop the tank and see what is in the bottom. Odds are, it's nothing.
I'd give this a wash as to whether it's worth it to replace the injector O-rings. Only because on 4.0Ls, it can be rather easy to cut them on installation.