The biggest battery hogs by far are the display and the radios. Sleep and Airplane Mode address those. Standby time for an iPhone 5 is "up to 225 hrs," while talk time and/or web browsing time are around 3.5% of Standby (up to 8 hrs.). Audio playback? 40 hrs. (18% of Standby).
Of course, your iPhone 5 cycles-up much faster than my iPhone 4, but even so, if you want to do something in a hurry (even if the radios aren't involved), waking from sleep is going to be faster than a power-up. In the end, you'll be less likely to power-down if the power-up delay becomes inconvenient.
Further, how often would you power-up to do something that doesn't involve the radios? If it's frequent, you'd benefit from being in Airplane anyway.
Personally, if I have to choose between wearing out a tool, and going to significant effort to keep it in near-pristine condition, I'm going to wear it out (not "abuse," not "neglect"). Life's too short. Any well-made tool that gets worn out will have paid back its cost many times over - it only wears out if you use it, and you wouldn't use it if it wasn't useful.
For battery life, I stick to basics, like reducing brightness, limiting push notifications and location services to things I need, no push email, reducing the auto-lock duration, etc. In other words, I focus on waste, rather than restricting usage. If I had to toggle Airplane (or WiFi, or cellular data) every time I wanted to do something involving them, I'd go nuts. For the cost of a few shrink sessions, I could have a new phone.
Apple recently overhauled their battery pages. They're worth another look
http://www.apple.com/batteries/
Oh, and of course putting it into Airplane (and locking the screen) is going to speed charging - it's going to charge faster if you're not heavily draining the battery. However, to what degree it'd effect charging is another matter. Actively browsing/transferring data over wifi while charging is one thing, wifi on while the device is asleep is another. If you're not actively using the phone while charging, the difference in charge time between Airplane/no Airplane is probably meaningless to anyone but a participant in some sort of race (...stop to fully charge, then move on to the next task...)
