Well I recall when browsing on Wikipedia, the Boukengers are stated to be 'based on a previous Sentai hero'. It's probably a Wikipedia vandalism that will be deleted soon as the only thing Boukenger is basing on is previous Sentai mechas on their monsters and enemies. But it was interesting to note. So let's go with how they compare...
1. Satoru Akashi (Bouken Red) -> Tsuyoshi Kaijou (Aka Ranger)
Okay, so... what's their similarity again aside of they're the leader and they're reds? I haven't watched Goranger, but I can be sure as hell that Tsuyoshi wasn't as adventurous as Satoru, nor did the storywriter at times treat him like a joke at times. They're both virtuous, I'd say that, but I think that's where the similarities end. This may be fine, but that's like saying Satoru is based on other old school Sentai Reds, preferably earlier ones.
2. Inou Masumi (Bouken Black) -> Gai Yuuki (Black Condor)
Right, so this one is probably one I can see making sense a lot. Masumi and Gai are the rebels of the team, they wear black, they start the rivalry with Red. It's easy to say that Masumi is based on Gai. Although, Masumi didn't bite the dust like Gai, and he's not so lone-wolf as Gai. Plus, he never fell in love unlike Gai. Aside of that, those were good points in comparison.
3. Souta Mogami (Bouken Blue) -> Hayate Sho (Change Griffon)
The only similarity I see is that they're both playboys, but aside of that they're really different. Hayate can be cheerful, but not as big as Souta. Plus... Souta is the tech geek of the team, while Hayate leaves the techies geeking to Sayaka and sometimes Yuuma! The hell?
4. Natsuki Mamiya (Bouken Yellow) -> Ako Hayasaka (Blue Swallow)
Again, just like above, they're of different colors and this is the first that I'd say they have... nearly nothing in common aside of they're the cheerful youngsters. Ako is LESS naive than Natsuki and much more tomboyish and leers to athleticism (until the end though), and hell, she's sometimes naughtier too! Plus Ako's backstory is quite the basic one compared to Natsuki. I kinda think that this looked like a job by someone who's bent on pairing Gai with Ako, and thus when they say Masumi is based on Gai, they say Natsuki is based on Ako! Seriously!? .... No, I'm not talking about you, Sean, I know you didn't edit that! Moving on!
5. Sakura Nishiori (Bouken Pink) -> Peggy Matsuyama (Momo Ranger)
*sigh* Where did this come into aside of they're pinks? Has it ever been said that Peggy was an ice queen as much as Sakura was before? Did she come from a rich family at least? Was Peggy being Tsuyoshi's vice-leader... or did she have a crush on him? You do know that coupling in Sentai started in JAKQ Dengekitai, right?? Where's the basis of this? *sigh* Editors these days...
6. Eiji Takaoka (Bouken Silver) -> Burai (Dragon Ranger)
It's just here because they're the token Sixth Rangers... and if that is the only basis, then I can say that Eiji is based on... Kou, Riki (Kingranger), Yuusaku Hayakawa, Hyuuga, *insert any Sixth Ranger here*. Let's get this straight, Burai's backstory was heavily linked with the Red Ranger of Zyuranger (Geki), while Eiji's backstory has NO connection with Satoru's. How did they come up with this basing!?
I swear, those editors were probably high when editing. Now... you ask who I think is based on who? I think you'd better wait till next time for that. Until then, see you later!
P.S: These are just opinions.