This is my opinion on all the rides that have Premier Access available on them and the likelihood of being able to save a reasonable amount of time on them that would justify the purchase of a pass (whether it's a One-Off or an Ultimate). Of course, these are just my feelings and others may see it differently, especially if they go at certain times of year that are busier (or at weekends).
Disneyland Park
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Peter Pan's Flight : HIGH - can get inexplicably long queues, but is same ride as in WDW, so you might not need to ride it
Big Thunder Mountain : MED/HIGH - if staying onsite, use Extra Magic Hours for much shorter queue but otherwise is worth the pass
Orbitron : MEDIUM - can get long lines for such a short ride but same as Astro Orbiter at WDW
Phantom Manor : MED/LOW - unlikely to need it, but I have seen occasional long lines
Star Wars Hyperspace Mountain : MED/LOW - seen it with both long and short queues. Note - thrill ride with inversions, so you might not want to ride it
Autopia : MED/LOW - even if queue gets long, come back an hour later and it'll be short
Buzz Lightyear Laser Blast : LOW - can get queues, but is same as Disneyland (CA) version so you might skip anyway
Pirates of the Caribbean : LOW - will take longer to walk the length of the (very long) line than time spent actually queuing
Star Tours : LOW - don't think I've ever spent more than 5-10 minutes in line here
Indiana Jones Temple of Peril : LOW - short thrill ride with inversions tucked away in a corner of the park that everyone forgets about so rarely a queue
it’s a small world : LOW - another where sometimes the queue will get long for no reason but that never lasts long
Studios / Adventure World
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Crush's Coaster : HIGH - if you don't get there at rope drop, it'll be a long wait otherwise
Twilight Zone Tower of Terror : MEDIUM - queues are common but line skip only gets you as far as Library, rest is merged with normal queue
Spider-Man WEB Adventure : MED/LOW - busy but has single rider line, tends to move fairly quickly
Ratatouille : LOW - has single rider line and three people per row, so it moves quickly
Avengers Assemble: Flight Force : LOW - thrill ride with inversions, plus a single rider line
Cars Road Trip : VERY LOW - not sure I'd even bother to ride this again, let alone pay to do it!
Opening at end of March
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Frozen Ever After : Almost certainly will be HIGH
Raiponce Tangled Spin : Hard to say, maybe MEDIUM just cause it'll be new
As you can see, there are a lot of rides I am rating with a LOW score, showing you that while the Ultimate Pass covers a lot, unless you're very unlucky with wait times, there's every chance you'd only really save any time on a small handful of them. Plus if you're not into rollercoasters with inversions, that rules out three of the rides you'd get a pass for as well.
The last time we were in DLP, it was supposed to be a quiet week but because of the Christmas decorations having just gone up, it turned out to be busier than anticipated - still not super busy, but certainly nothing was a walk-on. We also were staying off site, so didn't have access to the Early Magic Hour (in which you can get so much done). Despite that, we only used Premier Access four times in three days - twice on Big Thunder (on different days, plus we also did the regular line three times), once on Crush's Coaster and once on Autopia, which I normally wouldn't use it on, but it had been down for a large chunk of the day and once back up the queue never dropped below 40 mins, but it was only 5 Euros per person so we thought "why not?".
