I don't know without really digging into it if there are differing rates for pre or post-roll versus mid-roll ads, but the other point of consideration is that the amount of money hosting services per advert delivered is incredibly small, and is generally accounted for per 1000 downloads, so it's less about the value of each ad slot as opposed to the difference in having 2 or 3 slots per episode.
On the question of skipping or not, they're embedded against the cue points I've set at the point you download the episode from Acast's servers I believe, so I don't believe they'd ever know if you skipped them or not.
In any case, a little bit of pocket money coming in makes the time and effort more justifiable to my family, if I can scrape enough off it to pay for a family day out once a month that might make the laptop focus during "TV time" and the recording session family abandonment easier to swallow!
Happy to take the ads off though if the Beeb folds me into the licence fee incomes!