I don't necessarily agree in the fact that the parts in the kits are better. and made for the tractor.
They probably use the same manufacture of parts that the owner could purchase, valves, hoses, fittings, electrical.
By the time an owner has rounded up all the parts and installed same, the workmanship is probably as good as the dealer, and the owner has the satisfaction, of saying I did it and I learned something.
The only advantage in the kits, is the assembly may go together with out any fuss, and doesn't have to measure and make the hose sets, etc.
Some people never do things for themselves, and rely on other people to round up the parts and do the labor, and they feel that the pkg is worth it.
Any common sense person with a little knowledge of mechanics and hyd in general could redo the complete tractor. You see this being done all the time by the post on TBN and with the help of many people here passing out free advice and help.
About the only satisfaction of letting someone else do the job, is being able to say I am glad I did not have to do that, and I did not get dirty, and did really good on my golf game.
Some jobs I know I can do but I let other people do, mainly because of time.
I would encourage everyone to do it your self and have that satisfaction.
Those that don't have the time and have the money to spend, then that is probably the only way to go for them.
Time is money to a lot of people and rightly so, because it is getting harder to come by it.
To those that want to do things for themselves, more power to you.