Developement of these bikes were done in the "bubble" period of Japans economic economy and like with most domestic products (some of the best CD players ever were made in the late 80's and still are to this date) items were made with no expence spared. Chances are your Sony Walkman tape player still works to this day yet your MP3 player dropped dead after 3yrs !
Brakes changed from solid discs to semi floating and calipers from leading/trailing to opposed and 4 pot , this was cutting edge racing technology suddenly on road bikes. Early superbikes like the GPz900r have a single sided leading caliper on them ! Suspension had Nitrogen gas remote reservours , pre-load, rising rate & compression settings , tyres were now full radial
Sp models came into production with further race proven parts like flatslide carbs , Box section Alloy frames & swingers , partial rearsets....... these all mounted up to a bike that could have the lighting ripped off and be competitive on track.
Everything made in this period is collectible, open that Technics CD player you bought on 1988 and view those Burr Brown DAC's , Black Gate capacitors and low noise regulators
Honda were moving towards production hand made/built bikes using exotic materials, they started with the RC30 , produced the NR750 and then the bubble burst !! 
So here are the prices of the bikes as they were released in Japan, (GBP @ todays exchange rate)
Suzuki GSX-R400R SPII 59PS@12,000 RPM : 764,000 Yen / 6,310.12 GBP
Kawasaki ZXR400R J1 59PS@12,000 RPM : 723,000 Yen / 5,971.74 GBP
Honda VFR400R NC30 59PS@12,500 RPM : 695,000 Yen / 5,738.81 GBP
Yamaha FZR400R IWG 59PS@12,000 RPM : 677,000 Yen / 5,590.66 GBP
Honda CBR400RR NC23 59PS@12,500 RPM : 649,000 Yen / 5,358.08 GBP
Not all these had USD forks or opossing calipers ! So the mid-price bike commands the highest coin in the UK and most likely that Suzuki is never even considered !
Cause 250's were also in the FIII racing series here are their prices
Honda NSR250R SP MC18 45PS@9,500 RPM : 689,000 Yen / 5,687.62 GBP
Suzuki RGV250r SP VJ21A 45PS@9,500 RPM : 617,000 Yen / 5,091.62 GBP
Yamaha TZR250 3MA 45PS@9,500 RPM : 596,000 Yen / 4,919.29 GBP
Kawasaki KR-1R D1 45PS@10,000 RPM : 559,000 Yen / 4,613.26 GBP
That's why there are so many NC30s about , for the sake of 6,000 Yen and using the same licence you had the choice of NSR250 or a VFR400 not that it was the best of the bunch just the most affordable. Of all the Bikes listed above the NSR & VFR is the most I ever see, can't say I have even seen the 400SP Suzuki as of yet
But the UK is not alone, used prices of VFRs are also the highest of these bikes here
But book prices are meant to be based on retail so I would always expect to see shops following these guide lines - they don't !Anyhoo, still not selling mine
MM!
