I am sure you checked their hours...but, just in case...they are closed on Sunday and Monday.
The store is very well stocked with most things as far as I can tell. I can't imagine anything better in Northern California. If you can't find "it" there...no one else with have "it" either.
It is true there's a ton of inventory "in the warehouse" but, as far as I know...the warehouse is right next door in the same building. Any number of times, the kind folks there have checked the computer and gone to the "back room" to get something for me. Since the suite next door is labeled "Western Depot Deliveries Only" or something like that...I think that's where the vast inventory resides.
It is worth the trip if you like "being among trains." Otherwise, their website is very accurate and will pretty much let you know what they have. I sometimes ride from Roseville (about 40 miles) to "be among the trains" and for the "thrill" of picking something up in a store rather than through the mail. So...it is really your call. I know when I moved down from Alaska I had to venture to the store from which I had been ordering...just to see what it is all about.
Roseville has Railroad Hobbies which does not come close to WD when it comes to O gauge stuff. I guess the other gauges are fairly well represented...but, it is not an "exciting" store to me. I'd rather ride to the Western Depot and pay MSRP because I can be assured the WD will have what I am looking for. Railroad Hobbies used to stock a fair amount of MTH stuff...but, it is now gone and Lionel dominates...I am not even sure there is anything MTH left there.
Just Trains in Concord, CA is an interesting store...but, I go there only when I am passing through that part of the world. I went there many, many moons ago to listen to Mr. Mike Wolf extoll the virtues of his about to be released DCS system. I am not sure I have been back since...because I can find it at WD.
I have to be honest and say WD is rarely my first choice for anything...unless I desperately need a "train fix" now! I mail order most things as the price differential is significant...MSRP + CA Sales tax is a stiff premium to pay in my book.
Don't get me wrong...those WD folks are mighty fine people. Friendly, conversational, and helpful. They did not have an item the last time I tried to phone order from them...and they bent over backwards to make sure I received what I needed as quickly as they could get it to me. They even "ate" the shipping because their website and computer system said they had the item and, actually, did not. That said...they still have the best web store I have ever found.
I hope that helps rather than confuses.