Even if you play another instrument, knowing how to play the piano is a beneficial assistance to your understanding of music.
Piano is a handy visual aid--the layout of black and white keys can remain in the mind's eye as a way to visualize the order of the notes and all sorts of other aspects of music.
Therefore it is important to choose a good piano. Having a keyboard or synthesizer is only a Second Best to a real, acoustic piano. A real piano has a certain resistance in the keys that give it a more sensitive tone and a special tactile and aural pleasure in playing it. (Of course, some of the better and more costly synthesizers do have a good piano-like "touch". If this is all you can afford, it's better than nothin'.)
How does one go about buying a wonderful piano?
First of all, good pianos have "souls." Each piano has a different sound. Which kind of sound do you like best? Do you prefer a bright sound or a mellow tone? Do you like a more percussive sounding piano, or one that has a "string" quality? You see: the piano is both a percussion (struck) instrument and a string instrument (it has strings). Playing lots of different pianos is a good way to start judging which tone and which touch you prefer.
Do not get a piano with a very hard touch, one that forces you to use force to push down the keys. Ouch! Your fingers will get tired, leave alone your arms. And you may end up banging forcefully on softer-touch instruments, when you switch to a new piano. You may like an "easy touch" piano (one where the keys go down somewhat more rapidly and easily, with less force). I prefer somewhere in the middle. Too light a touch on the keys may make you a "lazy" pianist who flubs on all other instruments but his own. Traditionally, and surprisingly I guess, a number of famous pianists in the past did tend to favor the easier touch. Is it any wonder? They could sound so much more virtuosic on such an instrument.
The best deals on pianos are not, I am afraid, in the piano showrooms. The prize finds and bargain prices are most commonly found in the homes of people (usually old) who have a great piano but don't know it's great, or who never actually played it themselves or who have children who once played the piano, but now have moved away. There is one catch to finding such a piano--you need to bring someone with you who is an expert. Someone who knows how to tell if the piano will need new hammers, new strings, has a broken soundboard (DON"T EVER GET a piano with this defect!!), needs more than just tuning, or can recognize the "find" when it's there, the piano with REAL ivory keys, the instrument with a magical tone (and YOU the one who is buying need to be the truest judge of what is magical and personal to you). Don't ever be forced to buy an instrument you don't "connect with." There has to be that feeling in you that this is YOUR instrument.
By the way, ivory keys are (fortunately) outlawed these days because elephants were being slaughtered in droves to get the ivory tusks and many types of elephants sadly are close to extinction. However, if you can find a piano old enough (but in good shape) to have real ivory keys, your fingers will be happy. There is a certain feel to an ivory key that "grounds" the finger without it being too sticky or slippery. Plastic keys on the better pianos are a close second. But real ivories! What a treat.
If you go to a Piano showroom, take your trusted expert (a knowledgeable pianist, a tuner, or teacher who knows pianos inside and out) with you too.
Negotiation skills are an asset when buying a piano.
Also, if you can afford to do so, invest in an adjustable piano chair or bench. Being able to adjust the height for you or any other player is a wonderful "extra".
Having a piano in the home is like having a good friend, one who is willing to hear you out at any time, one to whom you can express any and all emotions, one who will bring friends and family closer together.
Enjoy your piano! Dust and polish it fairly often, and tune it ideally twice a year. Once you have moved your newly purchased piano into your home, it should be tuned right away. Be aware that drastic changes in weather can affect the tuning. Ask around for a really good tuner. A great tuner is worth his or her weight in gold!
Love your piano and it will love you.