From 8i to 9i and then 10g, Oracle is make more and more parameters to be dynamic at system level to reduce the downtime of your database servers. Following are some new parameters compared to 9i, I omitted some parameters that I am not familiar with.
Oracle memory:
sga_target
java_pool_size
SQL Optimizer:
cpu_count
optimizer_index_caching
optimizer_index_cost_adj
optimizer_mode
optimizer_secure_view_merging
star_transformation_enabled
Parallel Execution:
parallel_max_servers
parallel_min_servers
parallel_threads_per_cpu
Others:
resumable_timeout
create_stored_outlines
skip_unusable_indexes
sql_trace
I don't think making the parameter SQL_TRACE modifiable at system level is a good thing, I remember that one DBA have set it on at system level on production database by mistaken, others are good improvements.