Is an intensive 4-week stay worth it?

Absolutely! You will be speaking sentances and understand what others are talking about. Learing another language is a wonderful experience because you will have serious conversations. Maximo's professors are patient and the classes are small, I found it relaxing and enjoyed working hard. If you want to improve the skills you'll develop over four weeks are going to be useful; this is a great opportunity.

Yes, it’s certainly worth it. You could opt for a program where you have classical (approx. 4 students per class) lessons in the morning (9AM-1PM) and return in the afternoon for individual classes (2PM-4PM), which would still leave you plenty of time to explore the town and its surroundings in the evenings and weekends. I did a 6-week stay in the summer of 2015 with only the classical lessons in the morning only having a little background in Spanish (and I started at Máximo from scratch) and found that at the end of the period I was confident in speaking Spanish to the locals and getting around town. So yes, I think a 4-week stay at Máximo Nivel can already get you at a decent level of Spanish.