I'm with you on that. I've found that 2-3 longer runs are sufficient, especially if you're consistent with your weekly mileage. I've tried doing more, but it just leads to fatigue and increased risk of injury. Quality over quantity is the way to go, in my opinion.
I've found that setting small, achievable goals for myself during a tough run helps me stay focused. It's not about being all rainbows and sunshine, but about breaking it down into manageable chunks. Like, 'just get to that next mile marker' or 'finish this hill without walking'. It's not rocket science, but it works for me.
I go by feel, but aim to be at least 2 min slower than my easy run pace. Works for me.