The Chaffee is definitely worth it. Not quite as fast as the T50, but packs a way better punch. It is so much fun to circle strafe much higher tier tanks and take them down, to their utter astonishment.
Tis true, the repair costs are usually higher than the winnings, and often it will only take a single big caliber hit to squash you... but the view range is the best in the tier and with the speed to zip from place to place on the map, it can definitely be a game winning tank.
Also, the Sherman line is one of my favorites. Just hit my 600th game in my M4 (dead even... 47% wins, 47% losses and 6% draws) and will never sell that tank.
Love my Jumbo too, but I recently switched to the fast firing 76mm gun from the 105 gun. Still love the mid-derp on my M4 but have been liking the accuracy and speed of the 76mm on the higher tier Jumbo.
And finally, yes, Type 59's may be easy enough to kill if you know the tricks... AND get lucky enough to catch them just right. I win more games than I lose in that tank tho... and even if I lose, the credits pour in like a jackpot busted slot machine.
Btw: A special starts this morning. 3x for first victory and some deals on premium consummables (just in time for me to stock up on automatic fire extinguishers for my big tier 8 tanks)