So this thread convinced me to go all in...
Yep, I knuckled down and bought all four games brand new, the last of which arrived today. The three PSP titles averaged about £18 each while the PS3 game cost £23, all free delivery. Not bad really, I was expecting them to fetch for higher prices than that. I also purchased a used PSP 3000 that's in great condition for £30, specifically so that I could play the three PSP games. I'd have honestly rather played the PS1 and PS2 versions of BokuNatsu and BokuNatsu 2 respectively, but obviously there's no easy means of doing so due to the region-locked hardware, so I had to settle with the handheld ports.
This thread also persuaded me to take up learning Japanese. I don't think of the BokuNatsu games as the reason for this, but rather the catalyst; becoming more versed in Japanese is something I've wanted to do for a long time and should have done a lot sooner, but better late than never I guess. It's been three months now and slow going, but I'm studying every day and definitely making progress. And this might sound weird, but I'm not actually going to play the games until summer arrives this year. Not only does it feel outright wrong to play a series of games so revolved around the summer season in the middle of this dank and cold winter, but I'm also hoping my grasp of the Japanese language has improved a fair bit by then. I know it takes years to become fluent so I'm not expecting miracles, but if I can learn enough to at least get the gist of things in the games and understand a little of what's being said, then that'll be good enough. I don't want to go into them completely oblivious of everything with the exception of the most basic phrases, and I think being able to read a little and understand a little of the dialogue will enhance my enjoyment of the games as a whole.
Also, there was some news posted today regarding the Boku no Natsuyasumi franchise, although it's not particularly positive. Kaz Ayabe, creator of the series, was talking on a livestream at Tokaigi some hours ago and revealed info about a cancelled project...
Boku no Natsuyasumi creator divulges past development of winter break-themed game
That sounds like a great concept to me, and it's a shame it never came to fruition. I do wonder what the future holds for the series. I get the impression that Sony isn't exactly eager to greenlight another game.