having gone from a 1200 coupe with a worked A14 (I know its not an A15) with high comp mitsubishi pistions, lightened flywheel, balanced, big cam and twin carbs that made around 80rwbhp and blew gearboxes with alarming regularity, to a 1200 coupe with a stock L16 (that was a little smokey) with twin Hitachi SU and a little 32/72 cam making 92rwbhp, I can tell you it is definitly worthwhile. The L16 drove like a V8 by comparison - effortless torque. The cheap, readily available and strong 5spd's make the conversion worthwhile in itself, let alone the extra grunt.

replaced that engine with a stock L20 with 76 cam and twin 40s. 108rwbhp.
replaced that with a moderately worked L18 with the same cam and carbs, higher CR and slightly tweaked SSS head = 116rwbhp.