Wasn't Slap Bang meant to be an adult version of sm:tv live? I remember a sketch similar to Chums called 'Beers'
There's plenty more discussion about Slap Bang on the SMTV thread that's going on. But yes, they had Challenge Ant but with pensioners, and Beers instead of Chums. The problems were a) if you already watched SMTV it wasn't as good, and if you didn't, who cared, and b) crap jokes and messing around are all very good for several hours on a Saturday morning,, but on Saturday night you actually want some proper jokes. Beers crossed the line between being a parody of a crap sitcom, and being a crap sitcom.
Win The Ads had far more emphasis placed on it in the early days (in fact the name Saturday Night Takeaway refers to the prizes contestants could 'take away') and I'm pretty sure that was to distract from the obvious Noel's House Party-sized elephant in the room.
As mentioned, in the first series Win The Ads was played throughout the show, whittling down a number of contestants to one winner who would play the game we know and "love" now. In those days it was probably more like Toothbrush than House Party, a lot of the live bits of business like the variants of NTV followed a bit later in the run, it was pretty studio-bound in the early days.
As they say in their book, they needed a hook for the series because Slap Bang was just stuff that happened with no reason for anyone to bother tuning in. I remember it was the result of an in-house initiative at Granada for any staff at any level of production to come up with ideas for new formats, I seem to remember it was a researcher who came up with the Takeaway concept and they got a massive bonus.
For me, although I loved series 4/5 at the term, in hindsight it's where a successful format started being tinkered with. The pace of the show started accelerating (partly because of the new Lottery-induced 50 minute runtime, most of series 3 was 55-60 mins). There also started being a much greater emphasis on dragging people out of the audience and gunging/ridiculing them, which the Big Pork Pie had started the previous year. With a year or two it seemed like the cameras were forever on the audience seating and it was literally a party that the viewers weren't invited to.
Yeah, Series 4 was where it started going a bit wrong though I would suggest Series 5 was where it started to list quite badly, when Guy Freeman arrived as producer and they changed the titles (which I seem to remember them doing mid-series) getting rid of the dancing trestle tables and bringing in that anonymous dancey theme tune and shots of a real house, which I thought was a stupid thing to do because it was supposed to be a fantasy world, not a boring real house.
It started to become a bit too impressed with its own size and scale a bit as well, NTV used to be a simple click of the fingers and you were on, but by that point it became this incredibly elaborate affair which was more about the technology involved and how clever it all was, taking an age to set up, with the victim themselves barely in it. It started becoming a show about the show.
Also in Will Wyatt's book he mentions meetings with Noel and I get the impression around that time it might have been the case they spent more time discussing who owned what on the programme than actually what happened on it.