You've already gotten a lot of good info. I think the carpet you were cleaning had some severe wear and will likely never look anywhere near like new no matter what you do to it. There is clear evidence of heavy traffic lane wear which means it has actually lost a lot of the fibers in the traffic areas. Once those fibers are gone they're gone for good. Cleaning will not magically return them and applying more prespray won't help either which leads me to my next point. Be careful when using a Hydroforce sprayer not to over do it. You can spray a massive amount of prespray w/ a Hydroforce in a matter of minutes. Don't hold the actual spray tip too close down to the carpet when spraying, because the closer you put it down the narrower the spray pattern of the jet gets. Hold it up high enough that the spray pattern will be pretty wide. I think this probably contributed to your over wetting problem as well.
As far as your wand losing vacuum at the slot. I seriously doubt your wand is obstructed, but it can happen. If I think my wand is getting obstructed I will flush it from the top with a garden hose and sometimes run something through the tube to see if something got jammed sideways in it. Most obstructions will be where the vacuum tube joins in to the vacuum manifold. I hold mine up to the light and look inside the vacuum slot and I wash my wand out several times a year.What I do think is that your machine was more designed with tile cleaning in mind. It's a lot easier to remove water from a hard surface than a carpeted one.
I don't know if anyone has mentioned it, but a 175 rotary makes a great preagitator and you can usually pick up a good one for cheap. Agitation reduces the need for excessive prespray, super high psi, and even high heat quite considerably, but I don't want to spend a whole lot of time doing it either. It just takes a few extra minutes per room and is way easier than manual agitation. You can also use an absorbent bonnet to post bonnet a job and greatly enhance drying times when needed.
Last thought I would give is that not all carpets are salvageable. I don't care how good you are, what machine you use, or how long you've been at this business. You use all the tricks you've learned over the years and sometimes it still just doesn't come out great. You sometimes just have to do your best. All carpets are most certainly not created equal.Some carpets just don't hold up as well as others. Cheap carpets are cheap for a reason and that most certainly is not one of your better carpets that you had this experience on.