I have  7' St. Croix triumph with a 3500 Daiwa BG mounted on it. The rod is a freshwater version and is rated for lures up to 3/4 of an ounce.

 

Despite the rating, could I use a heavier lure sinker combination, i.e., about 11/2 ounces?

 

Is this rod and reel combination suitable for inshore fishing in lagoons, creeks, bays or do I need a heavier rod that is specifically for inshore? 

Your reel is a good choice for inshore, but I would use a saltwater rod, and no you do not want much over the weight the rod is listed at. 

 

The only difference in the salt and fresh triumphs are the components. The SW rods are more resistant to corrosion.  

A MH can handle 1.5oz but it's not ideal.  A H would handle that weight without being over powered.  I dont like to bomb anything over 1oz with my SC MHs.  

Are you throwing bait or artificials? If artificials then it's best to get a rod that can handle a little more weight then the max weight you plan to throw.  Every rod has a suggested weight range and inside range theres a smaller optimal range that the rod performs the best with called "the sweet spot."  The MHs SCs I have are rated .5-1.5oz but the sweet spot is 5/8 to about 1oz.  For example the older 7' M power SC I have is older and rated 1/4-5/8 and the sweet spot for them is 3/8-1/2.  Once you get towards the upper end of the suggested weight range the rod doesn't respond as well and feels overburdened.  That makes it harder to work baits that you have to twitch or pop.