Modification Nightmares

jax2 is correct. Mods done well are a very worthwhile improvement. If you can not do them yourself, then the aftermarket folks are a good way to go. the only word of caution I will offer, is you usually won't get your money back out if you mod a cheap piece and then try to sell it.
More expensive gear will usually give you a better return.
Also depends on what mods were done.

As an example, I have cheapie Parasound Zpre1. Sound quality is so-so in stock form. Add 400 dollars worth of vishay resistors to it, upgrade the coupling caps; and another 150 bucks for an oversized outboard power supply, and all of a sudden you have a reference quality line stage pre amp, that will compete with some really serious gear.

Now if I were to decide to sell the mod'ed zpre, I doubt I would get much of my money in parts back out of it, since everyone thinks its just a in house music piece.

To further Tvad's point, you need to 1st ask yourself
* why are you wanting to modify your equipment? i.e. what is wrong w/ it? or, what is deficient?
* when the equipment is modified, what do you expect to achieve sonically? (this is of course related to the question above).
* if the piece of gear is flawed, is it flawed sufficiently, is it better for you to sell it off & get a better model or switch to another manuf?

You can search the archives here & you'll find many names of modification houses depending which piece of gear you are interested in. Read their comments & find out what they think of the overall experience.

Modwright (Dan Wright) has been top notch in quality and service before and after the sale. He provides fair pricing and excellent service. As already said, if you decide to sell equipment you've had modified, you will not likely recoup the cost of the modification. You're much better off to buy used gear that has already been modified.

I had a ARC CA50 modified by Great Northern Sound. Steve is a great guy to deal with. Modifications were done in timely manner and there was great communication. I wouldn't hesitate to use or recommend GNSC.

I can 2nd GNSC. I also had a good experience with Bolder Cable.