I've been using the L35 Ghost Spider and got all kinds of feedback for the last couple of weeks on the level 77 Nike as I was thinking of upgrading. Finally reached level 77 Monday and hummed and hawed as there were positive and negative reviews like there are on every club.
Decided it was worth the 2000 credits and purchased it. I personally love it. I think it's a big upgrade over the 35 Spider, whether or not it's big enough over the 51 Nike only you will be able to tell but if it was me I would take the plunge.
Every now and then I would miss a putt with the Spider that would get a wtf reaction....so far no such result with the Nike....ball seems to stay truer and if I miss it's because I misjudjed the break. Also find that if I miss the ding by just a little the short putts will still drop where they wouldn't with the spider.
Of course i've only had the club for three days.....you may still find it in a pond by a green at some point in which case you could get a mangled putter for free.
Esty