Since yours is the only excellent Nunu guide that's also viable for higher Elo matches, I'd like to know what you think of the following points:
1) Masteries: Ardor is bad.
It's much worse than you'd expect, especially for a slow attacker like Nunu who furthermore can't get much AP anyways. Instead, I'd suggest taking 3/3 Resistance and and also 3/3 Strength of the Spirit and 1/3 Defensive Mastery and 1/3 Harden Skin (the first point here is twice as good as any further points, possibly a typo?). At 1000 mana (a level 9 Nunu with BV), 3 points on Strength of Spirit will provide the equivalent of a Regrowth Pendant, a 435g item.
2) Runes: Dodge Seals (+6.75 dodge %) are simply better than Flat Armor Seals (+12.69 armor), even more so later on.
Mathematically put: A Nunu with 20 base armor and 6 armor from Hardiness will have 20.63% physical damage reduction. With 9 Flat Armor Seals he will have 27.9% damage reduction, with 9 Dodge Seals he will have 27.38% damage reduction, plus a threefold increased in the Nimbleness proc rate. If you buy a Cloth Armor or a Doran's Shield for your first item then the increase in the % damage reduction is even higher from the beginning. Of course, dodging has the drawback of unreliability but its advantages simply outweigh that over the course of the match. Your other Runes are okay, but I still prefer magic penetration Marks and (sometimes) AP/level Glyphs.
3) Jungling route: I think there's a faster way to do it with the same camps as you do.
If you start at the small golems and Smite+Consume one of them, then run away until the second golem turns around, then start hitting the second one (you'll lose less health that way), Consume should be ready again exactly as you hit it down to 500 health. Then you'll level up (Ice Blast) and can do the Wraiths a lot quicker (Consume big one, Ice Blast a small one, perhaps Consume the last one before it dies). Then you can do the Lizard (and get BB) and gank.
This is not my usual route though, as I always go for a fast Dragon kill (or bottom gank) which I almost always get (with the help of one of the bottom laners so that I don't have to level Consume a 2nd time which would be a total waste imho).
4) General tips: When ganking, look out for enemies that do not have Flash, because they could Flash-dodge your Ice Blast.
Also, use Blood Boil on your teammate when ganking early, the additional 11% movement speed will let him close up much faster. Sometimes it's even worth to wait a few further seconds in the bush so that BB is almost usable again before ganking.
Use pings to inform your teammates of your gank and to mark your intended target.