If you can make it a Saturday you will see the rare Sheffield Midland - Cleethorpes Via Brigg service
I wouldn't call 3 services in each direction once a week rare. It's actually a regular service! If it was rare, it'd be something like once every 7 years, not once every 7 days!
As has been said, freight coming out of Immingham does tend to pretty much stop (may keep the odd coal & iron ore flows to Scunthorpe running, but that's about it) at around lunchtime, but there's still loads to come back, plus regular light engine shuffling about, so it doesn't completely die off, it just tends to mostly be in one direction.
By the way, Barnetby isn't a junction. That title belongs to Wrawby Junction.