Welp, since this thread was raised from the dead and it's the first time I'm seeing it... might as well add my 2 cents here.
When it comes to what the OP asked... quite frankly, the answer is "it depends". It depends on mood and time. Sometimes, I love to sink my teeth into a good combination of smut and gameplay, and sometimes I want to prioritize the smut over everything else. It's not a "one size fits all" thing for me.
I spent an ungodly amount of hours playing Venus Blood Hollow, collecting ALL the damn units and all their titles and all the damn items and so on and doing various dumb shit in the game and messing around with divisions and battalions. I exhausted the smut content for the game very early on, yet I still spent ages just playing and having fun. I've loved games like Alien Quest Eve and Night of Revenge, which are pretty damn heavy on the gameplay, regardless of the amount of smut they have on the side, essentially.
Yet, even then, I can still enjoy and appreciate games like the ones made by ONEONE1 and Acerola, where the gameplay mainly exists to complement the smut.
All that said...
I think the importance of gameplay depends on what kind of game you're making and what kind of story you're telling with your game.
Star Knightess Aura for example makes the gameplay basically part of its story-telling, what with the extremely limited resources and the impact of various choices on Aura. It integrates everything into one cohesive whole that works together. It's not perfect (nothing ever is), and it's an amazing experience if you can appreciate all of its elements... but I can't really blame the people that can't enjoy it because it's ultimately a hard game to figure out.
So how important is gameplay and/or grinding?
In truth, not at all. There's a reason why classic VNs are still popular. Some people just want semi-interactive stories without needing to worry about gameplay. Just reading and choosing.
What's important is putting something together that you can work on with passion, and understanding what kind of target audience you're making your game for. You can't please everyone. The perfect smut game doesn't exist. Even mediocre games have their niches for when you just want to play through something while your brain is turned off.
That doesn't mean people shouldn't aim for excellence... it just means that they should remember that one man's treasure is another man's trash.