Its not a cunning Lapierre ploy, i work for the distributor and our zesty demo bikes are all 514s 😆
We shift similar numbers of each every year. You do get quite a bit more bike with the 514, Carbon rear end does shave a good chunk of weight. The fork on the 314 is a good solid performer but the QR15 FIT fork is one of the best on the market and the bolt through does make a difference if your a more aggressive rider. Pro pedal shock is an upgrade but not really a necessity as they do pedal nicely without. Ive got one on my Zesty which I occasionally switch on on fireroad climbs but only if i remember! XT Wheels and tubeless setup on the 514 is nice and the Hutchinson Cougar on the front is one of the best trail tyres ive ever used. Whether all this is worth £500 really comes down to your budget, as its probably a fair price to pay for the upgrades.
314 is in WMB in the Trailbike of the year test which is out next week so that might be worth a read but whichever you go for you will be pleased 🙂