Since you've been burned, are you considering a non-iOS tablet? I haven't been too pleased myself with how poorly my iPad 4 performs with iOS 8.
Short Response:
I'm starting to lean away from an iOS tablet. iOS limitations can be irksome and Apple's seems to decrease performance more than increase features and capabilities. Right now I'm looking at the new retina MacBook as I want a more portable device than my 15" rMBP. I don't know if you've tried Windows 10, but it looks
really promising which makes me think about a Surface Pro. The issue is I'm heavily invested in Apple's ecosystem and while I
can work Windows in, it won't be as seamless. I'm debating whether I want to give up the tablet form factor, and whether to go Windows or OS X. And even if an iPad Pro is released, I'm not sure I want to gamble on another first gen iPad device.
Forgive this long response, but I'm trying to answer honestly.
Your situations parallels mine. I got my iPad 3 in June 2012. In September 2014 Apple released iOS 7 and I got a noticeable drop in performance, but I (bitterly) adapted. iOS 8 made it dramatically worse; embarrassingly slow. This iPad cost me $856 in total and I am angry that I got burned in
just 15 months.
I, like you, am hesitant to pay a premium for another iPad. Their functionality has evolved very little, but performance has dropped significantly. I don't like how cutthroat Apple is about iOS adoption. You can stay on your current iOS, but unlike OS X you will NOT receive any support unless your device is on it's capped OS; think of all the people who were forced to jump from iOS 6 to 7 because of that network security issue. Also, Apple really pushes developers to update there apps and many that I use tend to drop support for older OSes fast.
I need (want) a device that falls between my 15" docked desktop and my iPhone. Right now that's an iPad 3 with a keyboard cover. I bought an Air 2, but was underwhelmed and returned it. Honestly, I'm looking at the new Retina MacBook. I realize it's priced high with that new product tax, but it fits my needs well and I need it now for graduate school so I'd be willing to buy it. Others on this forum call it an "iPad with a keyboard," but with increased functionality. That's exactly what I want. I've had a few occasions where i still had to bring my 15" rMBP to campus because the iPad was incapable of doing the task I needed of it. Couple that with iOS' pitiful keyboard support, bugs, and frustrating oversights and my once most used device category is looking like it's about to be axed. I do like the iPad and will keep the iPad 3 around for occasional games, but as far as investing a lot into it? I'm doubtful. Once I graduate I may buy a cheaper rMini just for a few iOS games or just get an iPhone 7 Plus.
I still vastly prefer OS X to Windows for a variety of reasons, but Windows 10 addresses many of those issues I had and looks to be a wonderful release. That has me considering a Surface Pro. The thing is, I'm invested heavily in Apple's ecosystem. From big things like OS X-only apps to little thinks like iCloud Reading Lists. I
can work a Windows machine in, but I'm debating whether I want to. For example, a key use of this new device will be writing and I'll have to repurchase some apps like Scrivener. Not a huge deal, but one worth considering.
Honestly, I'm considering the new Retina MacBook. Yes, it is priced high because it's new. Yes, it "only" has the performance of a 2013 MBA, but for a casual office use and we browsing it's perfect. The biggest thing I'll do with this system is write. You mentioned in another thread (I think it was you, forgive me if I'm wrong) that you preferred the chicklet style keyboards Apple uses. I do too. I had to use an old mechanical keyboard for a few hours last week and found it much more fatiguing than Apple's offerings. As long as the new MB's keyboard isn't an issue (I don't think it will be), this will be a great device. I'm just waiting for in depth reviews before I make a purchase.
I'm going to wait until at least WWDC before I make a purchase so I can see where iOS is going. I just don't know if I want to give up that tablet form factor which can be very valuable, but I also don't want to wait for an iPad Pro that may never materialize (I'm more skeptical on it now with the new MB). Also, I bought the "new" iPad and got burned and I'm not sure I want to buy the first gen iPad Pro. With the new MB, there isn't really that much new aside from an already used Core M processor. An iPad Pro will have a larger screen and (supposedly) greater functionality and I'm very hesitant to buy that in the first release. I also don't want to wait 1.5 years for a device I need now-ish.
*Whew* Sorry. Was that too long?
It was a simple question, but one that involves many variables.