What would be involved in updating Hersey II’s to Hersey IV’s?

Since the Heresy IV isn't out yet and there are no specs on the Klipsch site yet (that I could find), it's a bit of conjecture.  I think I read in one of the threads about the Heresy IV that it will be a ported model, so I think you would have to do more work than it's worth to take a II to a IV. 

The II is well regarded, and many seem to like them better than the III.  You can buy aftermarket crossovers (or kits), and can replace most of the drivers.  Bob Crites offers great parts at reasonable prices.  There are some other options for aftermarket crossovers for Klipsch speakers designed to "improve" the sound (not sure about the Heresy II).  I have stuck with Crites parts.  I have upgraded my Heresy I by replacing the woofer, tweeters, and crossover, and putting Dynamat on the outside of the horns. 

As someone else said, give them a try stock, mine were very nice when I bought them, and they were about 40 years old when I got them.

Klipsch has forums with a ton of information about upgrades and mods.

There's a bit of hyperbole in both of the previous quoted statements.  Klipsch speakers are abundant and there are a number of sources for upgrade parts.  My KLF-30 speakers were a lot easier to listen to after I replaced the original tweeters with aftermarket parts.  I'm not sure if the crossover upgrades made a lot of difference, but they were 30 years old and it seemed like a good idea and was pretty reasonable.  A bead of Titebond III around the back panel kept them from rattling at high volumes.  An inexpensive and worthwhile upgrade/repair.

My Heresy I speakers sounded really good when I bought them.  I replaced the woofers mainly because I had some spares that I had used in the KLF-30s.  The Bob Crites tweeter upgrade seemed to give them a little more detail, and applying Dynamat to the outside of the mid and tweeter horns seemed to make them more cohesive in the mids and highs.  I replaced the crossovers because the ones from 1976 were definitely showing their age.

Were any of these upgrades game-changers or take them to a level way above their price point?  I don't think so.  Was it a waste of money?  I think I put maybe $500 into both pairs of speakers and they definitely sounded better after the work I did to them.  To me, it was easily worth it.  A lot cheaper than some fancy cables or power conditioners or many other things people do in their quest for improved sound quality and probably more impactful than most other upgrades would be for that amount of money.

You either like and appreciate the Klipsch sound (especially at their price points), or you don't.  If you don't, then the "lipstick on pig" analogy makes sense.  Why try to fix something you don't care for in the first place?  If you do and want to get the most out of them, upgrades are worthwhile and inexpensive.  Perhaps others have experienced more dramatic improvements than I have with their upgrades, but my advice would be to have realistic expectations in regards to the results.  The Klipsch forums have a wealth of information about upgrades.

I have been listening to Klipsch for over 30 years and they just arent my cup of tea.

But you keep listening to them?  I don't get it.

I do get that the Klipsch sound is not for everyone and have no interest in trying to convince someone that they're missing something.  I like the Klipsch speakers I have, but I own and have owned a lot of other brands, many that had a quite different sound signature and liked most of those too - Vienna Acoustics, Harbeth, Legacy Audio, Canton, Focal, Monitor Audio, Spendor, and others. 

I like some of these a lot better than Klipsch.  That doesn't diminish the listening pleasure I've experienced with my Klipsch speakers. 

If I thought they sucked I wouldn't listen to them for 30 years.  I don't see myself ever purchasing another pair of Vienna Acoustics speakers.  If someone was asking about different speaker choices and asked about VA speakers, I'd share my impressions, both positive and negative.  If someone already liked them and was posting about them, I wouldn't jump in a thread and tell them their speakers suck.  I also realize we all have different ideas about common courtesy and that mine may be different than yours.