I suspect the 1.4 is a little under powered and will be definately worked harder than your old 1.6 8 valve.Having said that,I suspect that reliability is more important to you than performance.
The 1.4 16 valve engine is pretty good to be honest,bar the infamous
problems.These aren't expensive to buy any more and are an easy DIY fix,you just need to carry a spare one around with you!.I'd definately make sure the timing belt has been changed as per the service schedule,it's due every 72k or 5 years maximum.
I'd buy as late a car as you can,even if it means going for a lower spec'd one.Be very carefull what you buy on
though,you can definately get some bargains and pick up cars that are priced much lower than they should be,but there are some dogs on there at times.Always go and have a look at them before bidding/buying,never be tempted to buy a bargain that is miles away as it's a very big gamble to take.
Scenics don't hide their mileage very well,high milers are usually falling apart inside and usually getting a bit ropey both mechanically and bodily.Automatics are best avoided,the boxes are suspect and are expensive to fix,there are a number of other smaller niggles which can happen but I'm sure you've experienced most of them with your old one.
Hopefully other Scenic owners will offer you their thoughts too.