It should be given pp because of several reasons.
1. It's a skill, and an integrated part of playing. There is no argument that can be made that will make me believe otherwise that someone spinning at 470 SPM is performing equally well to someone spinning at 300 SPM.
2. It affects score. A player with a higher score due to something that requires skill should be awarded something even if that something is very marginal. I don't see this value being very high, at least for sane spinning SPMs. If someone averages near what osu! can get for a max spin, then a point given per spinner is reasonable. Given that 1 mod added gives more than that, it would work out. (Obviously the value would change based on length of spinner).
3. At the rate most players spin the bonus would probably be less than 1 pp per spinner and close to nothing near the SPM considered easy to obtain given the OD.
4. Makes beating a score with a better spin rewarding.
5. Gives more points to Incognito, one of the best spinners in osu! Check
this map. Adding HardRock isn't enough to take the number one spot. There are people in top 50 who get more points than four mod plays. Spinning ability is certainly more impressive in this map than playing it with all mods.
6. Removes point ceiling on maps. An SS can be worth more points with a better spin.