I never get bored of the park... yeah, I get bored of certain rides sometimes, or feel like I can't be bothered to walk all the way to Air/Oblivion and then through its queue. What happens is that I feel fine about missing certain rides in a day/weekend (i.e. it's not unusual for me to not ride Air at all over a weekend trip, or only ride Oblivion once or something), so I spend the day doing things that interest me more without feeling guilty that I've come all the way there and not done certain things.
Then when I do go on Air/Oblivion, I find it's not so boring.
I find having an annual pass allows me to enjoy the park/resort a lot more and do things I wouldn't normally do. If it's absolutely humping it down with rain by midday/1pm, I have no qualms about hopping on the Monorail back to the Hotels and sitting in Ma Garrita's or the Dragon Bar with a hot drink for a few hours. Many a visit I've spent a couple of hours sitting and having a laugh in the Tavern with a beverage, and I don't mind sitting down for a meal at Rita's Chicken and Ribs and whiling away an hour like that.
If I went back to my annual trips, I wouldn't be able to enjoy the park in this way.
One of my favourite memories of Alton Towers was a lovely sunny day back in April 2007. I was with the TTF gang, and we just took a couple of hours, found a large spot of grass in the Gardens in front of the Conservatories, and we just chilled out, took in the views, chatted and had a laugh and it was so lovely. A Picsolve employee ;) came and took a picture of us, and it was framed in the Towers Street Picsolve shop for the rest of the season because it was such a lovely shot. I'd really love to take a big picnic basket with loads of goodies in to sit with in the Gardens on a nice day at some point... unfortunately, such lovely days weather-wise are few and far between now. :(
Yeah so anyway I digress - I wouldn't swap having an annual pass and having these lovely relaxed days, for going back to once-a-year visits and having all the excitement and build-up, however much I miss it. So basically, I'm saying, you may get bored of certain rides, but it just frees up more time to enjoy everything else the park has to offer. And it helps if you have good company with you too. :)