It depends upon how much you're willing to spend on your hotel per night.
For the last couple years, my RPR rate has averaged around $250 a night, but that's because we always bring my parents, resulting in a $50 a night adult fee ($25 per adult). Without that, the rate would be $200 nightly.
Never pay rack rates! Check for
AAA and APH (Annual Pass Holder) rates. In the past, the money saved by booking with the APH would cover the cost of the APH. However, with the increased price of the APH, that's less likely, but still possible. So your best bet will probably be AAA. There's also a "Stay More, Save More" rate that could be available during your visit: the longer you stay at the hotel, the lower your rate drops.
As for the benefits of staying on property, I believe that they are very good:
1. Unlimited access to the Express Pass line. Excludes Harry Potter And The Forbidden Journey, Pteraddon Flyers, and Hollywood Rip Ride Rocket.
2. Easy access to Citywalk and the parks. Each Universal Hotel has a dedicated walking path so there's no worry of crossing intersections. Also each Universal Hotel has a boat to transfer guests to and from Citywalk. We use the boats frequently.
3. Early entry to IOA/Harry Potter. Hotel guests can get in an hour earlier than regular guests. Some off-site hotels can also offer this perk if the guest purchased a Harry Potter package.
4. On-site hotel guests are allowed to pool hoop to the other Universal hotels' pools.
5. Priority seating at the Citywalk restaurants. This will usually cut your seating wait down significantly at dinner time.
6. Package delivery to your hotel.
7. Nice variety of restaurants. The following restaurants are located at RPR: Emeril's Tchoup Chop, Jake's Bar (opens at 3pm), Islands Dining Room (buffet), and Orchid Court Lounge & Sushi Bar. They also have a luau (Wantilan Luau) on Saturday evenings, that costs extra.
Hopefully, other posters will be along to point out benefits that I overlooked.