Is YUS5 as good as an upright gets? How does it compare to a grand piano?
Probably not. There are vertical pianos that offer more, but the further you go up the price ladder for a vertical, the less you get in return for your additional outlay of money. Certainly the YUS5 is an extremely competent vertical and second to only the SU-7 in Yamaha's extensive vertical lineup. It would not need to be as good as it gets to be a wonderful piano to learn on.
We had been considering buying our son a U3 when he outgrows his Clavinova CLP 340. I think the time might come sooner rather than later. He had a go at playing on a grand piano recently and it sounded so good!
The difference for a learner is not so much in how he sounds, but in the playing quality of the action. There's a lot of debate about whether a digital holds back a learner, but most would agree that at a certain point, a learner is better accommodated by an acoustic piano if he is learning classical lit in the traditional way. When that point occurs is the heart of the debate.
When looking at the Yamaha website, I found the YUS5 model. All the reviews seem to suggest that it's an excellent piano.
Whether our son (and daughter) will progress far enough to actually appreciate the difference, only time will tell. But we don't want to get the U3 and find ourselves having to upgrade later.
At a certain point in development, a classical learner is best (ideally) served by practicing on a grand with good tonal output and a good playing action. Again, it's not so much how it sounds to listeners. It's a function of the control which a grand action permits the player to have in manipulating tone. If the grand is mediocre in tonal possibilities and action quality, my opinion is that the YUS5 would be the better choice, but that may be a minority opinion.
Do these two pianos depreciate a lot in value? I ask this because a second hand piano would also be an option if it does.
I assume you mean the Clvinova and the YUS-5.
On the Clavinova there is generally a lot of depreciation. Digital stage pianos (portable) can fetch good prices used because they are needed by a lot of performing musicians on a budget, but cabinet consoles are a tougher sell. You might get a generous trade-in from a Yamaha dealer however.
On the YUS-5 5, it's hard to say. Probably the most attractive used piano on the market is the U-1. It's a standard bearer for the class. The U-3 doesn't lag far behind in broad cross-market appeal. Above the U-1 U-3 range, you would need to find a buyer who appreciated the fine points of the particular upgrade and was willing to pay for them. Those buyers are in a minority because most buyers of used U-1 and U-3 pianos are parents looking for a safe used choice for youngsters learning. The U-1 and U-3 have built quite a reputation in satisfying that demand.
The biggest factors in depreciation are how much you paid for the instrument and how you take care of it. Obviously, if you pay 11k for a new U-3 and I pay 9k for mine, I have a big head start on minimizing depreciation.
How many years of study does your child have under his belt?