Question on Stock Racing Tires and Kits.

Hey everyone. I recently just got into modeling. I used to build kits when I was 12 years old, but being so young and not haveing the patience to wait and let paint dry my models always turned out rather horrible looking . I have been buying the really cheap kits (the $15 ERTL and Revell ones) to practice on and get the feel for things again.

My 1st question is on kits themselves. Are the more expensive $40+ kits more quality made? I ask this because buying the lower priced kits I have noticed that a lot of the parts dont actually fit right. Certian pieces just do not like to fit in their little slot or is a little too short and wont reach the actual slot it is supposed to fit into. I am haveing to sand some things down so I can put a dab of glue on and have the next piece sit level. Another instance, is one kit I built, it said if useing the custom engine option to glue wheel assembly to the upper option of the chasis. Well this cant even be done because the wheels actually hit the wheel well. Once I get the feel for hand brushing again and buy an Airbrush I am going to work on the more expensive kits, but I would like to know if I will be facing the same problems with those too.

2nd question:
I am now in the process of building a NASCAR Nextel Cup car and just started to put the tires toegther. Well these wheels will just not go into the tires at all. I actually gave my thumbs blisters trying to get them in; the rubber was just so thick and hard. This is what I had to do to get them in: I was forced to get my Xacto knife and cute slits in the back of the tire so that it can give a little bit and still with a ton of force finally got the wheels inside the tires. I looked through the instructions to see if there was something I was supposed to do, but couldnt find anything. What is the trick to getting these wheels assemble? I never had so much trouble

Thanks in advance for your help