I have ended my used lens rave for now and ended up with three new lenses; 50/1.7, 28-135/4-4.5, 70-210/4 and a UV+Pol filter for the 28-135 (72ø) for a total of 285€. The 70-210/4 I got at eBay despite the warnings but a lesson is sometimes better learned on your own, it had a little ding on the edge of the front lens
But I got the 28-135 from an ad so I could see it for my self before buying it, and it was in mint condition almost never been used and still in its original case
Those are all Minoltas from '85-'86 and is a big step up in quality compared to the kit lens.
Conclusion - same as your advices
Next up, save for a new prime lens at the low end.