When I was starting out with this, I decided rolls were my friend. They’re great because there are so many simple things that can be done to replace them, and so many ways to replace notes with a roll. They’re the swiss army knife of simple ITM variation. 
One thing it seems to me I’ve noticed in the last years is not all tunes get the same amount of variation, so to speak. I’m thinking of the recordings of Peter Horan’s playing. It seems like some of his tunes – “Boys of the Lough”, “Devils of Dublin”, and “Kiss the Maid Behind the Barrel” come to mind – are just huge streams of melodic variations around a basic framework. Other tunes – usually simpler tunes, like two-part single reels – seem to have much more restrained variations.
Any notions if this is a common pattern, just a Peter Horan thing, or if I’m imagining the entire thing?
You know Kelly I think not being pleased with what you do is par for the course - for the next couple of decades, and maybe longer 
If you don’t feel like this, you won’t improve very fast.
I experienced chronic low-level (and often acute) dissatisfaction with my fiddle playing for the longest time. I think I started to feel happy with the way I sounded at about the time I reached a plateau where any more big leaps forward were unlikely to happen. Then you just accept who you are and what you sound like, and work on consolidating your own style and making the tunes you play your own.
Until you get to that (complacent?) spot, listening, yes. In your situation and mine that means records. An obsessive kind of listening though, giving your full attention to every detail. I remember at some early stage realizing I had recordings of about 8 different fiddle players doing Farewell to Ireland and about the same number playing Jenny’s welcome to Charlie - and I knew almost every nuance of all of them by heart.
Also I think it’s very important to listen obsessively to other instruments in the tradition, not just whistle players.
Anyway give yourself time, take the long-term view. If it takes 7 years of listening, 7 years of practising and 7 years of playing to make a piper, I don’t think whistlers or players of any other instrument will get off much lighter. When you’ve been playing a tune for 10, 15 or 20 years, paradoxically enough you’ll have no problem making it interesting.
Take heart, you’re doing really well for someone who’s been at it such a short time.
Steve
PS And don’t forget, you don’t have to vary like a virtuoso to play the music well. You’re out to play the tunes, not to show how inventive you can be. If you make a good basic statement of the tune, then tiny little changes here and there are enough to show you’re not asleep at the wheel - and keep the listener from falling asleep too.