I30N Perf could be had for just over 19k new at the end of the year - makes a hell of a difference to those comparisons. Half the price of a TCR makes you really need to obsess about perceived plastic quality 
you'll be lucky to find any Hyundai dealer willing to sell you one at around 19k. Coupled with crap finance rates and low value at 3 years the monthly figures just aren't worth it.
I'd be impressed to see that £29k car (we are talking the performance i30N and not the £26k standard i30N aren't we?).
If that kind of saving can be had, even if it's only worth £10k at 3 or 4 years old, that saving has covered half the depreciation. Add that to the fact you'd only be financing on a £19k car, you'd still be quid in vs 4.9% on a £33-36k (after discount) high end Golf. You save even more if you need to finance and get a cheap bank loan instead.
I'd seriously consider a £9k loss over a £20k loss for a same sector car that looks to be as capable, but a bit cheaper on the interior.
I've no doubt the TCR will be a more satisfying car to own, it's just a pity they jacked the price right up to cover the Akropovich exhaust that almost no-one would've specced as a £3k option. Luckily 0% finance takes the sting out of that decision by VW.
Hopefully the interior of the i30N is better than the old standard. My mate had a yellow Hyundai Coupe years ago, I dubbed it the "Aldi TT", which annoyed him no end when it caught on with our other mates.
