Yeah, a 1A diode would be fine. IIRC, the Spektrum draws around 300mA. Diodes, being simple, rarely fail unless driven to over their current rating. Putting two in a 2p arrangement won't help if one decides to short (the shorted one will bypass the other paralleled one). You'd be better off getting a single 3A diode instead if you are worried about it, just be aware that the less current you draw, the less voltage drop there is. A 1A diode running at 300mA will drop around 0.82v (and dissipate ~0.25w), while a 3A diode running at the same current will drop closer to 0.7v (and dissipate around 0.2w). Whatever you get, I would get 2. That way, if one doesn't drop enough voltage for your liking, you can just add another one in series. A package of these (or similar) would be perfect:
http://www.radioshack.com/product/in...ductId=2062578
Also be aware that the battery charging pigtail should be placed
before the diode (between the diode and battery) or the charger won't be able to read the battery voltage, and even if it could, it would read ~0.7v lower than it really is. Also don't forget that the Spektrum display will read ~0.7v less than the actual battery voltage.
When you wire up the diode, make sure the cathode (the end with the white line) faces the radio circuit. If you hook it backwards, the diode won't blow or anything, but the radio won't work.
If you happen to have an assortment of suitable NPN transistors laying around (who doesn't), you could tie the collector and base together, and then use that connection as the anode and the emitter as the cathode.