We are all fellow users on here and not Apple employees so have freedom in what we say and opinions expressed.
I fully agree that it can be frustrating to have to make replacement decisions when a piece of equipment is working fine. I have an iMac G5 that has been working great since 2005...but the operating system is way out of date, and now the computer is starting to act up so have decided to go ahead and replace it. Also have a MacBook Pro that is great, iPad, iPod, iPhone, PC laptop and Sun Sparc workstation, so your compatibility questions and concerns are very familiar.
If your components are playing nice at this point, keep doing what you are doing, in the engineering world we have an expression, If it ain't broke don't fix it.
As to the iPad, that device can be wonderful or just a toy according to how you decide to use it. It is almost a computer in itself...I say almost because you cannot just download applications other than those in the app store, and some things like word processing are not quite as straight forward as with a computer. But with AirPrint, if you have a compatible printer, you can seemlessly print directly from the iPad.
I carry mine almost all the time, and often on travel do not bother with the MBP. The wealth of apps makes it a very powerful tool. The downside, in addition to not having certain applications I want to use, is the virtual keyboard. It works well, but for my hand size is slow to type on.
Best advice on that score is go to an Apple store or reseller and spend some quality time up close and personal with an iPad and get to know it before purchase. And keep in mind it is very powerful but is not intended to actually replace a laptop in every function.