When I started flying I had no intention to take it any further than a PPL. Hence my hour-building was spread over about 18 months. I found that having an IMC rating reduced the amount of cancelled flights by around 90%. Because I passed my PPL in 45hrs it meant I could do the IMC and still have 100hrs P1 when I got to 150hrs TT, thereby not requiring further funds to build my P1.
I still have no plans to go for an airline job (wouldn't pay the mortgage!), so instead of doing the ATPL exams I did both the CPL and IR. It's probably about 80% of the work of the ATPLs. I knocked the whole lot out in 5 months whilst holding down a full-time job. By the way, I also flew about 50hrs during that period. Flying 4 or 5 hours a month isn't going to put a big dent in your study time.
Just depends on your lifestyle really. If you're happy to commit to 15hrs study per week it's not such a big deal. As the idea of going out "into town" at a weekend makes me want to vomit, I spent many a Saturday night with a bottle of wine and a big stack of boring books. It can be done, but it's all about compromise and planning.