Honestly, there's a point of diminishing returns. I kept trying to upgrade from Goldring NS1000s based on whatever was the current forum FOTM. Always ended up disappointed.
At the moment I usually use Goldring DR150 or NS1000s for everyday, HD600 for best. I also have a set of MAudio Q40s for a passive closed headphone that doesn't leak but generally prefer the NS1000s. Also have some Sennheiser IE6s. DT770 pros and A900s have been and gone, along with numerous other highly rated headphones that just weren't much better than what I already had.
Of course if you're spending a lot it's always worth trying before you buy. There's always the odd set that comes up at a price that's worth trying on spec because you won't lose much if you sell then on.
However, I will say that HD598 (which I tried in a store ) to HD600 is quite an upgrade