I have to give this a visual +1 - a "like" just isn't enough.
For me, trying it once (with success) was fun. I have not made time in my "experimental" brewing to try it with a common style - but it wasn't based on the outcome of the spiced ale. For me, boiling "just the hops" doesn't save time in the brew day.
Like @flars said here,
I have skimmed over a similar thought in various places. This, from How can I get better hop utilization? back in 2007,
On the surface this [ How can I get better hop utilization? ] may seem like an easy question. Since hop utilization decreases as wort gravity increases it seems logical that one solution to the dilemma faced by extract brewers who boil concentrated wort is to boil the hops separately. This may sound attractive but one downside to this is that the quality of the bitterness and the extraction of plant substances from the hops are reportedly different when hops are boiled in water compared to boiling in wort, and the differences are not for the better.
seems to summarize my "book knowledge" on the topic.
The suggested "different" hop bitterness (suggested in the article), in the right recipe, may be a difference for the better.