Whether RE262
requires an amp is a personal decision.
What Clip+ has is low output impedance, so it does not have an issue with driving most of the demanding gear out there. It is
flat with frequency response (some players do well without load, but not with a BA like TF10 attached). This is the reason I still keep Clip+ around, though I wish I had a more powerful, flat sounding source. The issue with Clip+ is low output power (18mw @ 16 ohms, I think). It is not the
loudest player around - Cowon D2 does -6.8dB and Rockboxed Clip+ does -11.6 dB with 16 ohm load. All other things being equal, most people would prefer a 'louder' source because of the ease with which they are able to listen to details.
An amplifier, is just not about power or increased SPL. An amplifier is about controlling the driver's movements. It can also bypass the not so good headphone out of a player and have desirable results with IEMs. You get additional clarity, resolution, better sound stage with Arrow 3G for most IEMs - be it the lowly BeB or the highly 262. Is the 'improvement' meaningful? Not in all cases. In some cases where your source is unable to drive the IEM / Headphone properly, an amp improves things for the better. In some other cases, there would be changes, but not as significant as in the first case.
Then, there's the question of IEM
requiring an amp. It is not always about impedance or the sensitivity of the IEM. RE1 has the same impedance of 150 ohms, but is much harder to drive than 262 - it will be happy to consume all the additional power you throw at it. Phonak PFE (32 ohm, sensitivity of 107 db/mW), an IEM with far better impedance and sensitivity specs than RE0 (64 ohm, 100dB/mW) shines similarly better with an amp. I'd say both of them do not
require an amp, but do better with an amp. RE1, to me falls in the "requires amp" category, RE-262 falls in the "shines better if amped" category like RE0. For me, the difference between amp-ed and un-amp-ed RE-262 is not such a significant enough difference to bother carrying an additional amplifier with 262. For my lower volume listening, 262 does just fine straight out of Clip+ at -15dB. So, if that's what you are after, you are fine without an amplifier as long as you can
charge Clip+ after every 5 hours of use. For Faheem and Brendon, what I call 'minor improvements I can live without' are important enough to always use an amplifier with 262. Who's right and who's wrong here? Nobody as both are opinions based on personal preferences.
I suggest a middle path - buy 262, try it with Clip+ and see if it works out fine for your convenience and your listening levels. Get an amp on loan and try it with 262. Then, you can A/B and figure out if the improvements are meaningful enough for you to not only spend, but to carry an amp everywhere. That's the only way this can be settled.