Sometimes this is really useful, say for travel or mapping apps, but you should turn off anything that you don't need. Apple's Stocks or Facebook for example may not be vital.
The same goes for Apple's Mail app - push email can be really useful but it hammers your battery, especially on a cellular connection.
In Settings > Mail, Contacts, Calendars > Fetch New Data, turn Push off and consider switching Fetch to Manual, which means you have to physically check for new mail, but saves a decent amount of power.
With each generation of hardware Apple tends to introduce a new feature that is hardware-dependent, but that doesn't mean that your older hardware is left entirely out in the cold. Often, third party apps exist to restore similar tools to older phones and iPads.
Siri for example only works on an iPhone 4S, iPad 3 or higher but apps like Dragon Dictation, Evi and Vlingo run on earlier devices and provide voice-based interaction of various kinds.
Only recent iOS devices support Airdrop, Apple's device-to-device file sharing system, but there are alternatives. There's Dropbox of course, which is an excellent file sharing solution, but also DeskConnect, InstaShare and Pastebot, all available from the iTunes Store.
These involve a little extra effort, typically signing up so that you can link devices, but generally work very well.
The iPhone 4S was the first model to directly support panoramic photo mode, but there are apps to let you do this on older phones. In fact there are loads, including 360 Panorama, Autostitch Panorama, Panorama Free and Pano. Many are free so you can check them out.
You will want to upgrade eventually…
You can't make your device as fast as the latest iPhone or iPad – there will come a point when the lure of that blazing fast new device simply becomes irresistible - but you can use some or all of the tips we have mentioned to minimize battery use and reduce the overall load on your processor and graphics hardware.
The good news is that these things really do make a difference and will help you to squeeze more life out of your beloved older phone or iPad.
By installing a few free or inexpensive third party apps you can also bring extra functionality in line with newer models so don't despair, help is at hand.