Huysegems is so slow and labored to turn, run, make decisions. Makes the transition bloody hard work. And his total reliance on his left peg is also irritating. Amazing he played a dozen or so games for Belgium.
Huysegems had good quality players next to him in the Belgian team which allowed him to do reasonably well in that particular setup. He simply was not the top player of the Belgian national team. Ditto Cunningham for Costa Rica.
Consider the aging but classy Alessandro Del Piero - he won quite a few games for Sydney FC singlehandedly last season, but can't win them all (and is of course well into his late thirties). Shinji Ono is younger, fitter, and certainly one of the top Japanese players of the previous 5-7 years. Our (WPX) imports are not their respective national teams top players. So I would not overestimate the qualities people like Huysegems or Cunningham (or Hernandez) brought to the Nix. They are good players but not good enough to turn a match by themselves. In his prime, Hernandez was probably good enough to turn a game around for Melbourne Victory, until he got slow and overweight and went to India. In his prime, Ifill could turn the game around for the Nix, and is an example of a key national team player (like ADP or Ono), it's just that Trinidad and Tobago are not in the class of Costa Rica let alone Belgium, Japan or Italy.
You don't have to be a "key" player for a national team to do well in the A-League which is perhaps English League One standard (certainly not Championship level). A decent but not outstanding player playing at a reasonable level (e.g. Ifill who was certainly no star at his clubs in England) often does well in the A-League.
Huysegems was a very good player in his prime and played for very good sides in Belgium (Lierse) and the Dutch Eredivisie (over 100 games for Feyenoord, Alkmaar and Twente). At AZ Alkmaar they were a top-three side at the time and made the UEFA Cup semis. He was signed by Feyenoord after they lost Kuyt and Kalou, to stiffen the attack. FC Twente finished as high as second in the Eredivisie in his time there and made the Dutch Cup Final.
However he's been dogged by serous injuries for a few years which saw him struggling to start games on returning to his original club Lierse in Belgium and so ended up here. The A-League would suit his attempt to regain fitness with the long off-season and fewer games then Europe. He didn't play 15 times for Belgium by accident, and sure, he was never its star player, but it was not a period when Belgium had a lot of good players.
Ifill showed early promise in England but was never a star player for any teams such as Millwill or Sheffield United, and though he played at a decent level, mostly in the Championship, by the time he caught the flight to Wellington, had been struggling with injuries and not getting game time for Crystal Palace.
By the way, Ifill was a Barbadoes international (somewhat inferior team to Trinidad and Tobago you have him playing for) and probably was their star player - although that wouldn't be hard (they lost 9-0 on aggregate to the USA in 2010 World Cup qualifying). He made intermittent appearances in only three years, 2004, 2006, 2008, mostly against the likes of St Kitts and Anguilla.
Kenny Cunningham and Hernandez were amongst the best players in the Costa Rican league when they played there and deserved their national team call-ups. Lets remember Cunningham played as recently as June in competitive matches for a Costa Rica side that finished second in CONCACAF WC qualifying.
Hernandez is certainly the only import we've had with a decent international pedigree for his country, and certainly was a major player for them. His international CV is impressive:
Costa Rica: 35 apps, 7 goals
The stats for him on Wikipedia are very incomplete - rather check out his page on FIFA.com here:
http://www.fifa.com/worldfootball/statisticsandrecords/players/player=182587/index.html
including: 2001 FIFA U-20 World Cup, Argentina (all four games incl. vs. Netherlands, Ethiopia, Ecuador and Czechs in the round of 16)
2004 Athens Olympic Games (all four games vs. Morocco, Iraq, Portugal and Argentina in the quarter-final).
2006 FIFA World Cup, Germany (2 apps in finals vs. Poland & Ecuador))World Cup qualifying: 9 apps in 2006 qualifying incl. against Mexico, USA, Trinidad, Canada, Honduras, Panama, Guatamala
(Costa Rica qualified directly as third place side in CONCACAF behind USA, & Mexico);
4 apps in 2010 qualifying vs. Mexico, USA, Honduras, El Salvador (called-up for the final round of qualifying & Costa Rica made it to play-off vs. Uruguay as fourth team in CONCACAF). Missed the play-offs due to injury.
International goals include in two World Cup qualifiers against the USA 2006, and a winner against France in a friendly in 2010.
His most recent appearances for Costa Rica were in three friendlies in 2011.
Shinji Ono is one of the top Japanese players of the last 15 years, rather than 5-7 as you say - appeared for Japan way back at the 1998 World Cup, signed for Feyenoord 2001 and would have played against Huysegems in the Netherlands. And like him, probably opting for the A-League's less strenuous demands after his career has been blighted by injuries for many years since his time at Feyenoord. Last played for Japan 2008 and would have more than his 56 appearances since his debut 15 years ago but for injuries.