Here is the list of features the 4700 has that the 3700 does not:
1. Auro 3D capable
2. 32 bit D.D.S.C. HD Digital
3. AL32 Processing Multichannel
4. Jitter Reduction
5. Bass Sync
6. One more HDMI input
7. Front HDMI A/V Input
8. One more zone
9. Composite outs
10. Two line front display vs one
11. Gold plated RCA terminals
12. Bigger Power Supply
13. 125 W per channel
14. Lower Analog Distortion
15. Higher S/N Ratio
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The features seem worth it to me. I would go with the 4700. Your preference may be different? The difference in features is not always obvious.
For instance, I really like the two line display versus one. There are several 4700 features I would miss if I moved to a 3700. But, if you didn't know what you're missing it might not matter?