Convincing a consumer to buy any tablet other than the iPad is a tough sell. The question then becomes which iPad to buy. Like any marketing machine, the margins are in the upgradese and accessories. Aside from a few special cases, the 16GB WiFi iPad gives you the most bang for your buck and only lacks features you probably won't use anyway.
Apple makes significantly higher margins on their higher capacity devices. When you can buy a 16 GB flash drive for $10 (admittedly a slightly different type of memory), it's hard to imagine it costs Apple $100-$200 more to manufacture higher capacity devices. Just 5 years ago it would've been hard to imagine being able to purchase a device that could do as much as the iPad with the storage capacity it has for the price it can be obtained. As consumers we get a bit dramatic in our expectations and complacency with technology that is often less than a year old… That's another discussion. Still, it's disheartening that the available iPad capacity options have remained the same 3 years in a row.
There are arguments made that you'll need more storage with the increased size of retina display enabled apps. Pish posh! There are few cases that require extensive amounts of storage. Gamers, media enthusiasts, and appaholics will certainly need some more breathing room. For the other 90% of us, streaming through Netflix, Spotify, and iCloud will leave more than enough room for plenty of apps and several large games. The market is shifting towards cloud based streaming services, leveraging these options means less local storage.
Achieving 20+ MB/s download speeds on LTE is liberating, but at bandwidth caps suck all the fun out of it. It's like owning a Ferrari with a 5 gallon gas tank that can only be refilled once a month. What's the point of having all that speed if it's short lived and you're always paranoid you'll hit your limit? $130 just to have the capability to use a built in cellular connection could buy you at least 4 months of tethering service on your smartphone. Tethering plans are just as easy to turn on and off every month as the iPad's, and don't extend your contract. The vast majority of iPad data use occurs where there's available WiFi anyway. Don't give cell carriers an additional pipeline into your wallet. Remember a year of 5GB/mo is around $600! You're better off buying two WiFi iPads!
iOS devices may very well have the most buzz and appeal of any product this decade, but that doesn't mean you have to spring for the most expensive model to join the party. There's no fancy insignia or a rear spoiler to indicate you're more classy or posh. If you're not an "extreme" user, go for the 16 GB. If the number 16 doesn't feel big enough for you, watch an episode of Hoarders.