Read Thread: Changing the type of box
Notice that "HIPS" is an attribute only for event stamps? If it's a HIPS, it's an event box.
The vast majority of them I've seen, if they have clues at all, the clues weren't needed to find the box. And while I have "searched" for them, I wouldn't call it an "effort." It just means I was casually "looking around for suspicious-looking objects." I wasn't following clues, and my strategy for finding them is very much different than a real, traditional letterbox.
I know not everyone agrees with me, but there's another reason I prefer them being listed as event boxes--it makes them easier to find online. They can be attached directly to the event so I can pull up a list of event boxes at the event and, "Oh! There it is!" And record the find.
When it's a traditional, I have more trouble finding the listing because first I'm looking in the wrong place ("why isn't it in the list of event boxes?"), then because I have to do a traditional search and I'm not sure how it was listed. Do I search for the park where the event was held? Is it listed as a "mystery" box?
So all things considered, I'd highly recommend listing HIPS as event boxes. They're meant to be listed as event boxes and I've even gone so far as to not record finds on incorrectly-listed event boxes because I don't want them screwing up my F-counts. I've never heard of anyone refusing to record an event box listing because they think it's really a traditional box and they didn't want the find to mess up their event F-count. =)
I know people don't like rules and regulations, but it does help find listings when people are following from the same playbook.
I do that too. I have a spreadsheet with "real totals" (which is sorely out of date, I am working on catching that up) which ignore things which didn't involve me needing to figure out a clue of some sort.