I just call and have room requests added to my room reservation. If you have a river view booked then you don't need to request that. If you don't then it is highly unlikely that you will get a river view and you 'wasted' a request. I usually request "as nice a view as possible" when booking standard view. We have had some surprisingly lovely views in standard rooms with that request alone. Meanwhile, room views are really not that important at moderates, IMO, as you have outside walkways going past your room. It really isn't something that you get to enjoy like at a deluxe with a balcony, so I don't get overly worried about the 'view' in moderates or values. We prefer to request top floor (less noise/traffic) and a location near the food court and buses (for convenience).
Touring plans does help a lot with making requests. We have had about a 50% (rough guesstimate) success rate with requests being fulfilled. I try to look at the worst rooms in a given category and book that category if I will be happy in those. If not, I change the category or resort. I have been known to end up in those 'worst case scenario' rooms! LOL! And it was fine, we still had a great time.