The later upgrades only appear if you already have the earlier ones.
*upgrade spoiler*
The order you must get them in is:
1. High-grip tyres - Nutty Acres Act 3 - 3 Jiggies needed
2. Floaters (and propeller) - Logbox 720 Act 3 - 10 Jiggies needed
3. Spring - Banjo Land Act 4 - 23 Jiggies needed
4. Scuba Seat - Jiggosseum Act 4 - 38 Jiggies needed
5. Laser - Jiggosseum Act 5 - 57 Jiggies needed
6. Horn - Terrarium of Terror Act 5 - 90 Jiggies needed
If you only see the high-grip tyres, then you missed the floaters. If you go and get them, all your other upgrades will be applied as well. I had this problem having acquired the horn before the laser.