Tiago,
Things may be different in your part of the world, but I always figured that the cost to REGISTER FOR, and GET TO/FROM a race outweighs most other costs ... including SPARES. You should certainly have a spare axle, axle tube, drum (front and rear), backing plate (front and rear), wheel/tire, tie rod (even if it has to be worked on to install), and possibly a rear suspension "trailing arm" (whether it's really leading or trailing), as well as a significant set of TOOLS
with you at every event. (Things you don't have, can usually be borrowed or bought from "competitors" at the track, but that doesn't help you at home)
When I spend 8 hours towing TO an event - the fuel to get there - the registration fee - and the fuel and time to get home, I have to consider what it might cost to have a spare or 2 with me. Maybe your tows are much shorter and maybe your entry fees are much lower, but $100 - $200 to have the spare parts to keep me in the event (after I've already PAID those other costs) is well worth it to me .. and that's for a single event. Hopefully, the spares will last you several events (or maybe FOREVER <G> and the amortization costs go to ZERO).
I also figure that .. if I have the parts on hand at the track, and
I'm already there, and
I have to/need to fix it anyway at some point, and
I don't have anything better to do at the track if I'm broken, and
I have the tools I need, and
there's often HELP available, and
my barmaid (wife) can keep me in 'spirits' <G>, and .....
Well, you can see the progression.
I've seen a LOT of guys/gals spend $700 on the 'get to/from', 'register for'. 'stay' (motel?), expenses and get NOTHING out of the weekend but a lap or 2. From my perspective, being prepared for "the event" includes spares and 'fix it at the track if possible' plans in place. If you have those spares "in the trailer", it also covers the situation you are in. Home maintenance. If you find a problem getting ready for the weekend, you already HAVE the spare on hand to fix it and you don't miss the weekend.
I know this doesn't help you in the moment with the weekend already imminent, but it's something to think about if you want to race on a regular basis.
I know that I have had over 30 years to acquire my spares, but I wish I had had the knowledge and intelligence to have those spares earlier in my "career". I would have "LOST" a lot fewer weekends.
As for your last comments. Potential HP loss is not a big deal, but REST ASSURED, if you do have trouble in the center section, it will only get worse as you race. And it's a pretty short path to damaging other $$parts$$ - unfortunately, this is my
experience talking ...
As usual, YMMV
Steve, FV80